I can't help with all of this but here goes.
I leave my computer on 24/7 and I haven't lost a fan yet. As for wiring it to the mains, I bought a 12v adpter thing with the right ampage and wired it straight in. The adapter has settings from 3.5v to 12v so if I want the fans running slower I just move the switch.
Outtake fans should be @ the highest and intakes @ the lowest I think but I could be wrong.