1. Again, without seeing the scene again, I can't really comment much further. It depends how long she was out, and I'd still have to double check to see if it was her or Kylo doing it.
2. It was very explicitly stated.
3. I think it was made clear that Finn's plan was not going to work. I'd also have to watch this scene again, but it didn't seem like he would have made it there, as his ship was already melting on the way. I'd have to see the scene again, but I'm fairly sure the implication was that he was playing hero for the sake of playing hero, and Rose saves him from an ultimately doomed plan.
As you point out, Luke had a meaningful conversation with his sister. And what did he say in that conversation? He said, "nobody is ever gone" (or something to that effect) before giving her Han's dice. The implication is obviously that people live on in our memories. Why give her them at that moment? Obviously, to let Leia know that he doesn't plan on making out alive. It's a more subtle, more aesthetic, and more memorable way to express his plan.
Leia knows Luke doesn't intend to make it out alive. So, what exactly would she have done? Luke can trust that Leia has common sense and is going to figure leave. And also, let's keep in mind, that Leia is literally the only person there who Luke knows and is the leader of the resistance. It would be weird for him to strike up conversations with a bunch of new folks.
I'm not saying it wouldn't have made more sense to say his plan explicitly, because it would have. It would have also been far less interesting. What was done still falls well within the realm of suspension of disbelief.
4. In the end of episode three, after Yoda says this, I'm 99% sure Obi Wan name drops Qui Gon. But, whether he does or not, it's clear what they're talking about. It's the very end of the prequels, so there's not going to be any payoff in that series, which means they're referring to something from the originals. Since the force apparitions are the only thing we see that relates to communing with the dead, that must be what they're talking about.
5. I never said that was exclusive to them. Neither Anakin, Yoda, or Obi Wan seemed to have the ability to communicate directly over a distance, aside from being dead.
Where does he get the ability? By practicing I guess. I'm not sure what you're expecting here. Are you looking for something like Naruto, where they introduce a new technique, and then have a 20 minute flashback for making of the technique? Like, a scene of him meditating and practicing telepathy? If that's the kind of storytelling you prefer fine, but that doesn't make this a plothole. If we did it that way, they'd never be able to introduce any new kinds of force techniques, like force lightning, in Episode VI which was also introduced suddenly and surprisingly. We haven't seen every potential force ability yet, and only a few that involve the dark side.
We also don't know that other people can't do this. It's not a particularly useful technique. They already have the technology to communicate over long distance which is far simpler. It's only used here because the Emperor is using it to draw Rey to him, and because Rey and Kylo have a special connection. But it's not like a replacement for cell phones.
Jedi being a myth makes about as much sense as the 1960s being a myth to us. Luke was born at the end of the Clone Wars, and he's in his mid 20s by the end of ROTJ. There have been 30 years in the interim, so we're at most 60 years removed from the Jedi order being a pretty big thing in the galaxy.
At the beginning of a New Hope, there are people alive who have seen and interacted with Jedi. Leia's father is one, and Jabba is another. And when Jabba coins the term "Jedi mind trick", no body seems to doubt Jedis are an actual thing. In Rogue one we see that there is a whole sect of monk like people who know of and use the force. A random smuggled may not know, but the even if there was a concerted effort from the Republic to stifle knowledge of the Jedi, it would have been nearly impossible to do so.
It's never stated, but Snoke's design definitely conveys age. He was quite likely alive during the Clone Wars. It's not unlikely at all that he'd have access to information regarding the force.
You repeated yourself again, but these still aren't plotholes. Some of these things actually were clearly explained but you missed the explanation. The one you keep coming back to is Snoke, but that's based on the faulty assumption that in a galaxy of millions, there can only be two people utilizing the dark side of the force, but that is never stated. It in fact seems highly unlikely that in a galaxy of at least millions (presumably trillions) there would be only two people.
...I keep coming back to all of these, because they all bother me to a degree (except for 2, although that brings up another issue that I tied into #4). I'm not sure where the claim that Snoke is the one I continually reference. And, again, I'm not sure what point you're trying to make by saying "these aren't plotholes." Are you arguing that these claims, even if my logic does hold up, aren't plotholes, or just that my logic is flawed and therefore it isn't a plothole?
#1: Then I'd invite you to look over it whenever you get a chance. I don't believe Kylo is ever shown during the scene, so I don't think there would be any reason to assume his involvement.
#3: Again, I'm not sure how it's any less interesting to say "Hey everyone, I'm gonna stall for time, get out." If you need a flair for the dramatic, he could deliver some kind of speech on how he's going to pay for his mistakes so that others can live, and that the resistance shouldn't repeat his same shortcomings. As I mentioned in my previous post, in what world does publicly addressing people suddenly become not cool?
Or, for fuck's sake, tell Leia the plan and she can communicate it to the rest of the resistance if he's so afraid of doing something "weird" in the middle of a life and death situation by talking to people he doesn't know. You argue that Luke could trust Leia to have common sense and figure out that she is supposed to make a run for it...but she doesn't. Poe is the one who figures it out, if memory serves. If it was left up to Leia figuring it out, the resistance would've sat there and burned.
#2+4 now: Keep in mind that the technique we're talking (or at least I was) about here is communicating over vast distances, not with the dead. So you're right that Yoda and Obi-Wan discuss Qui-Gon and some technique he's discussed, and that it's probably the force ghost thing, but that has nothing to do with the original issue; which was how Luke managed to project himself across the galaxy.
You mentioned in a previous post that: Luke however, unlike the others, still has something to do in this world. So he is able to partially give himself to the force, essentially leaving him halfway between life and death, which is why his force apparition is more corporeal.
Unless I missed something blatant in the movie, this is just speculation, at which point, yes, it does become a plothole. When a certain established character or power somehow gains the ability to do something which they were unable to do before without a stated or easily inferred explanation as to why, it becomes a plothole.
I'll reference a previous example of what I would argue is a similar "plothole by absence of information," or something that is a plothole because of the lack of an adequately stated reason. Retro Studios acknowledged a plothole in the original Metroid Prime involving Space Pirates ran into a creature that other lore seemed to suggest would have been difficult to reach because they were having trouble getting inside the location where the creature was when Samus finds it. There could've been a myriad of inferred explanations for this; perhaps the creature simply found a way out of its cavern that the Pirates missed, or perhaps it has some unstated teleportation power, etc. Despite all the possible explanations that could have been made by fans, it was acknowledged as a plothole by professional storywriters and ultimately changed for subsequent re-releases. This sort of plothole by absence of information is very much a plothole.
Which brings me to...
#5: To put it plainly, I'm searching for some explanation as to how this extremely powerful guy, with incredible mastery of the force and powers that we've never seen before, just showed up with no explanation whatsoever and suddenly took command of the remains of the Empire, all while never being sensed by either the Emperor or Darth Vader. Keep in mind that, in Episode V, the Emperor was able to not only determine that there was a new force user alive, but also that he was Darth Vader's son. And that was based on the limited ability Luke had developed up to that point. As far as I know, the force doesn't work like a cell phone network, where you can only detect things if they're within a certain radius. And, if it is for some reason, there should be an explanation why. Correct me if I'm wrong, but I had kind of thought the idea of Anakin bringing balance to the force was the entirety of the force, not bringing balance to the force within your 10 light year radius and only until some other evil asshole shows up from the next galactic cluster over.
This falls into the issue of plothole by absence of information. Imagine if, say, there was a sequel to the Return of the King where some villain even more powerful than Sauron showed up with no explanation as to who he was, where he came from, or why he didn't show up before, and started commanding the same army Sauron did. We'd be thoroughly criticizing that, and yet here it's somehow excusable.
To the other points within #5
A: I'm more talking about where he learned the ability. Is there some secret dark side support group on the opposite side of the galaxy that just somehow went undetected during the entirety of Palpatine's reign? Again, plothole by absence of information.
B: I don't think it's ridiculous at all. To borrow an example from history, the Azerbaijian government, through propaganda and historical negationism, had essentially erased the Armenian Genocide from public memory by at least the 1980s, a mere 65-75 years. The example that you mention of us not knowing what the 1960s were like today...was reality in certain parts of the world, and may very well still be.
Admittedly, there are differences between the two situations. The Empire has a lot more ground to cover; it's presumably harder to control information for an entire galaxy than for a single country. But, simultaneously, when I say "myth" I don't necessarily mean "never existed at all." More like the tales of people using the force are just fabricated and the Jedi were some group whose stories were exaggerated to be things that weren't really the case. I think this is reasonably well supported in ANH, when one Empire council member (not sure what the position title is) refers to Darth Vader as having a "sad devotion to an ancient religion." It's pretty clear that he doesn't think much of the force, and I suspect the same is true of Han. I have no doubt that there are some people/beings who interacted with Jedi beforehand, like Jabba, who believes in the force (although tbh I'm not entirely convinced he wasn't just mocking him), but those people are likely in the minority.
And additionally, if it's been 60 years since the Clone Wars ended, then it's not unreasonable at all to assume that this could be a minority. If you don't properly begin remembering things since you're about 6-7 years old, then at youngest anyone who remembers the Jedi at this point will be 66-67 years old. The vast majority will likely be dead by this point. And given the absence of the Jedi ever since, they aren't being replaced by many eyewitnesses who can attest to the Jedi's existence. With the control of information that the Empire and now the First Order have, that's bound to decrease the number of people that know of them significantly.
All of that to say, it would be really difficult for Snoke to access information surrounding the force, especially given the Empire's control. Even more difficult to access information surrounding the dark side.