As far as I've heard it will be out for PS3 and Xbox360 only.
I predicted somewhere on the article that exploring and collecting supplies will probably be encouraged, simply because it makes sense and makes the whole story more realistic.
That hasn't been stated or announced, but i don't think it will happen. The only playable character seems to be Joel. I liked how they made Gear of War: Judgment, where you can assume the role of all the team's members, it's a totally new play style and it will probably be used more in upcoming games.
Yes, the game is really realistic or so it seems from the short gameplay trailers.
Could be. However, there's a lot of expectation about PS4 games and this seems to be an upcoming title for PS4.