You have arrived at the right place but you may want to post on the car side p15-d24 forum to get a little more responses. I have owned 2 p15 and they are great cars. As to wiring if you plan to enter Plymouth culb sponsered meets you may want to go with a premade correct wiring harness but if you are looking to save some money then you can rewire with modern style wiring but you still need to use the correct gauge for 6 volt. I rewired a 52 plymouth a few years ago just replaced everything a wire at a time with new style wire.
As to cleaning the bottom of the car I think you could wait on that for a while, 1st thing after a good tune up is to get the brakes in good working order.
For now get a service and parts manual and read all the information on the home page of this web site use the menu on the left
http://www40.addr.com/~merc583/mopar/framesets/welcomeframeset.html