What else to buy ? Can't say at this point, take it one step at a time, try to make an agreement with him that you will probably be buying more from him in the future.
If connectors are corroded / damaged, learn how to solder a new connector ( that you get from him ) to your old harness using shrink-wrap insulation.
Get a good soldering pistol ( Weller ) some good rosin core solder and lots of shrink wrap of various sizes.
The proper way to connect two wires together is to strip each at about 1/2", cut a piece of shrink wrap to about 3/4" and slide it on one of the wires, cross the wires at the center of each stripped section and twist them to each other. Solder using the minimum amount of solder that completely covers the connection, let it cool for 20-30 seconds, then slide the shrink wrap over the section and apply heat. If you see you are gonna be doing a LOT of this, get a good heat gun also.
DO NOT TRY TO DO THIS WITH CRIMP CONNECTORS, YOU'LL REGRET IT IN THE FUTURE !!!