My 1996 Wells Cargo Auto hauler with beaver tail and ramp door is built like a tank. I have carelessly hit the bottom rear driving into and out of steep gas station driveways and it has suffered no damage. It does not happen very often because the driveway must be quite steep.
The beaver tail makes loading and unloading all cars, especially low sports cars, much easier .
In addition to the other excellent suggestions here, I will second the motion that it should have a driver side door to allow you to get the car door fully open. Without the driver side door, you can barely get the door of a big '50s or '60s car open. If you are lucky, you will be able to barely squeeze your way out.
It should be serviced before long trips to help avoid problems on the road. Brakes, bearings, electrical connections, lights.
I carry two spare tires, just in case I run through a construction zone in the middle of nowhere.
A tire pressure monitor system will alert you to tire problems.
Don't tow with a tow vehicle smaller than a 2500 pound pickup or suburban. I tow with a motorhome and the dual rear axle provides great stability.
Equalizer bars and an anti-sway control system are musts, even on a motorhome.
A maximum speed of 65 to 70 mph is a comfortable speed and about as fast as you will want to drive so long as you have loaded the trailer properly with sufficient tongue weight. If you load the trailer with low tongue weight, the rig will wander back and forth and you will scare the hell out of yourself, at which time you will stop, move the car forward and increase the tongue weight. I travel with about 1,100 pounds of tongue weight and it trailers straight and solid. The tow vehicle and trailer should be level.
A CDL is not required for a 12,000 pound trailer here in Illinois or in most states that I am aware of.
Hope this helps.
Best regards and good luck.
Ed Leed