I think i will go for the Litecoin mining.
Whats the max GPU's i can have per computer?
Whats the best OS to install on the computers?
Do i need to spend a mouse,keyboard,lcd for each computer? Cant i make some sort of cloud for one computer?
You only need one single mouse, keyboard and monitor for all of them. You don't even need an hard-disk, an usb pen drive with Linux or CraPE (somewhere in this forum) will do. When set up, use a vnc server or remote desktop to login to the machines without needing to connect mouse/kb/monitor
Consider these ATI cards:
7950: 175€ - 200€, 650 Kh/s
6950(used): ~110€, 450 Kh/s
5850(used): ~60€, 400 Kh/s
7990: 520€ , 1200 Kh/s (bad €/Kh ratio, but higher density)
Offtopic: are you from Lisbon ?