I'd run 0 or 00 for cables if coming from the trunk and be sure to ground to the engine, and then run a ground to the body. The engine needs the direct ground.
As far as the fans, I would say that there is no way the current fan setup is enough. I also doubt that the setup you linked will work with an FE, the water pump is very close compared to a small block. Hard to make make room for room for a single centered electric fan and motor
That being said, it is hard to beat a stock style fan for cooling if it's a street motor. May want to consider it with the current radiator for a while, then if really desired, look for dual Spals as big and bad as you can get