Corsair PSU's are known to be very good, you might be able to save some $ and get a less powerful one, someone with more knowledge can hopefully help with that. As for compatibility issues, you might want to look into picking up a cheap processor to get the computer to boot and update the BIOS if it is needed.
Check out Gomez Peer
on how to make your PC work for you. Referred by dark2099 please!
Mini Rig: Biostar TP67XE / i5 2500k / Corsair H55 / 2x4GB PNY / XFX 7770 / Corsair CX500M / Win 8 64 bit / Thermaltake V9 Blackwidow