1. there are many distros for different things and different people. you will have to decide which is best for you yourself. I am a SuSE user and i beleve that it is a great all round os, and is quite user friendly. if you are new to linux you should stick to the most popular distros because there would be a larger user base and therefore you will be able to find help more easily.
see here
http://distrowatch.com/dwres.php?resource=major
2. i have played a few linux games and they ran as good as any windows game, but please take note of my specs in my sig below.
3. no you cant realy play windows games on linux, though there is an emulator (cedega) that make play possible and i've heard it works quite well. but i prefer to simply run my windows games on windows.
4.i have never done this, and surely it can be done but probably not without some tweeking.
many people say linux is not game friendly, but it is the games that are not linux friendly. game developers just dont port their games to linux. why? because windows holds approximately 95% of the desktop and it may not be profitable for them to port it to linux.
i use both linux and windows on the same computer. windows for games and linux for everything else.