Yuuki, I wont quote because Im too lazy.

1. Windows 7 is a mix of windows XP (which almost everything is compatible with) and Windows Vista (Which has a good looking, but not as compatible). I just built mine, and Windows 8 IS AWESOME.

2. To this kind of build, a small tower is more than enough.

3. Calculate and find out how much PSU you'll need, dont just go for a 500~600 when you dont need more than 300~350 (Ex.)

Also, I'll post a new build to you, _RemiX and Red later.