While choosing, make sure the car you desire can be matched to an available base plate for the tow bar that you want to buy or already have.
I wanted a DEMCO tow bar setup but no base plate was made for my car. I had to buy a Blue Ox instead.
Then, once you have decided on a vehicle, ask again on this forum , for a response from someone with experience towing that make and model. They might be able to give some specific additional info.
EX: my Chev Sonic hatchback with 47 cu ft of cargo space plus an addition crossbar roof box setup offers a lot of extra storage that can be flat towed. GM says to pull a fuse every time you hook it up. Reason being, it will prevent the discharging of the Chev battery while the ignition is 'ON' while towing. A simple solution to not have to do that every time is to add a 12v charge wire from the RV to the car to charge the car battery.
You don't really need to buy specific harnesses to run the car lights.
Its less expensive to drill a hole in each tail light assembly to install an 1157 bulb for running, brake and directions. Just run those wires to the front of the car to incorporate into the tow harness going to the RV. If you decide you also need side marker lights etc, just turn them on via your dash switch and run with them on the parking light setting. Your charge wire will keep your battery charged as if you're driving your towed car.