Power Mac G5 server with ATV and 2 Macs running 10.6

I need a little advice please!

I currently use my iMac as my main computer for iTunes, it has my entire music collection and a few movies on it.
My ATV is set to sync with my iMac. The ATV is modified so I can also use my external drive via USB which has a large collection of movies on it.
I access my external drive over my network through the ATV using Cyberduck etc.
This isn't an ideal set up. I'm thinking of buying a Power Mac G5 running 10.5 server and using this for my iTunes library and transferring all the movies from my external drive to the second HD. I could then presumably just use my iMac and MacBook as "slave" devices, streaming content from the server and also the ATV would look to the server for sync.
Would this work? Could I access files stored on the server from ATV using AFP?
Could I remotely log in to the server and access files over the internet?

I guess I'm basically looking for advice on setting up a server, some guides maybe?
Any compatibility issues with snow leopard macs and leopard server?

Any help greatly appreciated

... also would I have to make iTunes purchases through the Power Mac? And would I need to plug my iPhone in to it or could I somehow still use my iMac to sync my music from the server to the iPhone?