first home server....confused???????????

hi all, dont know if this is the right place to put this, but there doesnt seem to be a real section on servers, so i apologize if im in the wrong

I've been thinking about investing in a home server for a while now, and since i recently came into some cash (its burning a hole in my pocket), i thought this would be the time to do it.
Basically this is what im going to be doing with it:
1: Most importantly; it will be a file server, mostly for movies and music, which at the moment is an absolute mess across about 3 computers. It will also be connected to the home theatre in the living room so i can access movies on the plasma without having to put them on disc.
2: I was thinking about running a client server setup, although a little research into this leads me to think this may be a bad idea.
3: instead of a client server, i was thinking of setting up a peer-to-peer using a gigabit switch. Problem is, i want it to be wireless so i dont have to go plugging in the laptops
4: I will also be backing up onto it, so should i go SCSI, RAID, NAS or other??????
5: What operating system should i use? I've heard a lot of people say Linux. I have ubuntu dual booting on 1 of the PC's, and im quite happy with that, so some opinions on windows vs linux would be appreciated.

I think thats all my questions (i know its a lot, but im still new to this whole server thing)
Thanks in advance