You can't add more soldiers like in Enemy Unknown? I believe Enemy Unknown you start with 4 but can bump it up to 6 later buy buying the perks in barracks. Didn't even know XCOM2 was coming out.

I feel your pain because I am still going through Enemy Unknown. Did the Ironman setting (I believe that is what it is called) where you can't reload. Was doing really good but then I lost most of my vets which seems to be towards the end of game. Now I am trying to get a decent amount of vets built up again.

Yea, I had a nice garage of vets but after two hard missions I lost all.  I have a few vets now but still set back from what I had.  If anything I could go your route and go down to the second difficutly setting and probably advance past where I am at now.  I had to do that in Fire Emblem Awakening actually (had to go from hard to normal difficulty) to progress and finish the game.  This is actually my second time playing through because first playthrough I didn't build the satellites quick enough and countries started leaving (could still probably go back and beat it later).  Current playthrough only one or two countries have left so far and I've invested in the intercepter weapons and have full satellite coverage now.  Who knows maybe I was near end mission and got wiped (now they are giving me a few softballs to catch up).  Game is hard to tell how far you are progressing but it doesn't bother me much because I'm basically just looking to battle.

I always drop to a lower difficulty when a game starts to piss me off. Then I go back to my original difficulty when I feel like I'm past the stupid stuff.

I don't have Xcom 2 yet (hoping for a Black Friday deal like Enemy Unknown had) but I'm likely going to set my first playthrough to novice when I do get it. I like to have fun at first, then to ramp up the difficulty as I get better. So if the game seems unfair, OP, I'd have no compunction about tuning down the difficulty. Games are supposed to feel fun, not cheap. 

my backlog is too big. 

i'll buy this game in about a year when i can get it for ~$10 on some flash sale.

Didn't bought it yet, I'm waiting for my larger PS4 HDD. So I'll give tips based on XCOM: EU/EW.

Anyway, XCOM can be quite hard if you don't plan it right. Priority 1 is increasing your cash flow. Then you go for upgrades to increase squad size and improve weapons. Upgrades to decrease the frequency of reloading are also a must.

Save and reload the game a lot. Don't let valuable squad members die. The best things in the start is to focus on getting a small squad promoted several times. Don't go hiring new soldiers, it's bet to have 8 people with 6 captains than having 20 squadies.

Don't try to advance too fast. Always leave 2 (at MINIMUM) soldiers on overwatch. Reload guns with some time in advance. After you clear a wave, stop and reload all guns.

If you didn't planned things right, you will probably face a seemingly impossible mission down the road. Don't quit, just save and reload until you pass through. Save after each turn if needed.

So you never play the game on Ironman settings?  You should see my graveyard...  It was pretty low for a long time then there was a pretty big increase.

Oh, the tips were created assuming he is playing on normal. On Ironman you really don't have much choice and people will die like crazy.