Of course real distances wouldn't be fun in this kind of game but here it's the extrem opposite with planets few kilometers away from each other. It completely breaks the immersion.

I'm honestly not really bothered by the always online since games like Diablo3, Starcraft II and others require me to be online at all times, that and playing them on PC with little down time is good enough for me so NMS being always online on a PC won't really bother me much.

For me, it'll ultimately succeed or fail depending on the main driver for the story. It's very hard to get a good story working in a procedural world. If there's no story at all, I imagine it'll get repetitive quite quickly.

1 - No.  There won't be gas giants, but there will be plenty of dead planets, toxic gas planets, ice planets, and whatever else.  Expect a lot of diversity.

2 & 3 - Not sure about orbiting.  I know there are night and day cycles so I assume there is some form of orbital mechanics.

4 - Yes.  It is incredibly rare, but they do happen in the game.

Any other questions?  I have been following this game crazy closely lately.

While this video doesn't exactly answer all the questions you've raised, its a really interesting dev interview and it gives some great insight into the way the No Mans Sky universe has been created.

This also has implications on how the universe will function..

https://www.youtube.com/watch?v=h-kifCYToAU

I think i ended up with more questions after watching it though

The planets aren't "saved," but what you do to them are. What you do to the planets changes it's "seed," which is saved to servers. The game is always online. The devs vision of the game makes it online only. Everyone is discovering planets together and uploading them online, so there can't be a conflict where two people name and change the same planet differently because one person wasn't online at the time.

The game is always online. 

I know it's always online. I was just commenting on the fact that he said it got uploaded to the server and saved.

I've been watching some more vids on this game. Here some of the stuff I learned. There's no tutorial. Each player starts on their own planet. If you're the first person to find a planet, you'll be credited for it. You can discover animals and plants. The closer you get to the center of the galaxy, the harder and more rewarding the game gets. Space stations function like cities where you can buy new stuff. Each space station is unique. You can write messages on the ground where other players will see it.

If you die in space, you lose your ship and will be sent to nearest planet via escape pod then you'll have to gather more resources to buy another ship. If you die on the ground, you'll respawn next to your ship but lose what resources you were carrying. You have to walk back to your ship when on a planet. There are twin stars but they are rare. There's no gas giants. The game could end up supporting VR helmets. There's night and day cycles on the planets. Any stars you see from the surface of a planet are other planets other players are on.

You can only have one ship at a time. You can kill/grief other players. Planets' surfaces are the actual size of planets. There's no npc's walking around. You can swim.

what about weather conidtion, or more importantly, extremely weather conditions? 

and different types of stars? or will they all be "sun like"?