If you want it to be easy, you can get your complete wheels at a place like Northern Tool. Probably not the cheapest place to search, as they will be close to $200 apiece (rim and tire). You might be able to piece something together cheaper at Discount Tire, but you should still expect to pay at least $150 per wheel.
The electrical connection from the tow vehicle to the trailer is going to depend heavily on the previous owner. When this trailer was originally built, the wiring for the whip probably was not arranged to today's standard. The previous owner ought to be able to shed some light on the situation, and should have the wiring lead. If not, then assume it is wired to the original configuration, in which case it is a bit of a bear to figure out in a hurry. I would suggest just getting a set of those temporary trailer lights that stick on with magnets and a LONG wiring extension.
If the trailer wiring has been updated in the trailer to meet modern standards, and is useable, you are still going to need to see the connection on the front of the trailer. Originally, it was a 7 pin round connection, in which case, you will very likely have to build your own whip with the round connections on the trailer end, and 7 flat blades at the tow vehicle connection. You can get the parts to do this, again, at Northern Tool, etrailer.com, various RV supply places, etc.. If you want to use trailer brakes, and the wiring is all correct, then you will need a brake controller in your vehicle.