Ahh-- make it stop!

The transistors do not have to be physically mounted far apart. They can be right next to each other, no problem. You just don't want any pins or tabs to be able to touch one another or touch ground somewhere on the car as that can short it out. You don't have to worry about fans as were not driving these like they would be in say an Car Amp circuit. "Do transistors add power like relays do?" I'm not sure what you mean. I've never seen a relay that Adds power. Unless you mean current, then yes, with a low trigger current, you can switch a much larger current through the Emitter & Collector Pins, just how a relay does with it's contacts that are rated for 30-40Amps. Transistors do not add power or have their own power. You are supplying +12V and Ground and the transistor is just responsible for switching that ON or OFF in this application.

yah, that's what I meant.  I just worded it poorly.  Thanks a lot man!  I'll let you know how it works out.