1) hey if you have money to burn dual 120.3s would be nice =)
Most car radiators are aluminum, so you want to stay away from that since you have copper blocks
2) Im actually looking to do the same thing (dual 2-342s and a lot of blocks) but Im thinking of going with dual MCP650s. Cathar is looking at a new 12vdc pump, Im waiting on the results on that before I decide though. The MD-30RX is the one people recommend IIRC. That would do your system justice Im sure.
3) I dont have any blowers so I cant help you there. If its not 12vdc or 115v ac then you are going to have to buy a powersupply of some sort unless its like a 24v blower that can run on 12v but at a lower speed... I know a lot of large DC axial fans come with built in controllers, maybe some blowers do also.
When you get working on it be sure to post a lot of pics
good luck