If my wheels turn out to be worth saving, my first upgrade planned was to switch out the old one fan, and install a dual fan setup.

My question is, would it be possible to wire one fan to run any time the engine is on, and have the other one kick in only when the temp gets up there?

 

Yes, however in the winter it will take forever for the car to warm up with one fan on constantly. I wouldn't do that. Read up on Willie's total fan control in the Cooling section and consider those options.