I'd say 24' minimum too.
I have a 28' that I found used in the local news paper for $6,000. It had several options like side escape door, so I can drive the car in and open the car door inside the trailer (with the trailer door open), also had the upper and lower cabinets up front, an A/C and Heater unit, 12-volt and 110-volt lighting, and exterior lights. I think the owners said it was also 6" taller than normal? This is a steel dual axle tag trailer and fairly heavy. I don't think I would want anything longer as a tag, would go goose neck to make it easier to maneuver, and put the tongue weight over the trucks rear axle.
When I bought the trailer it had 15" rim "D" load range tires which I did not like because most of my cars are over 4,000#, plus the extra weight of tools, parts, generator, pit bike, and all the other stuff that gets thrown in the trailer, I think the total weight is at least 9,000 to 10,000 pounds. Those tires would bulge out on the sidewalls pretty good even at 80-psi. Anyhow, those tires got change to 16" rim "E" load range tires.
My Ram has the towing package, so it had a receiver and pre-wired for the trailer connector and brake controller, just needed the brake controller.
Used the Tekonsha Prodigy P2 Brake controller which you can order with a wiring adaptor for the Ram so you don't have to mess with wiring the Ram connector to the brake controller universal harness.
I got the load leveling trailer hitch with the trailer, but no sway control. Trailer sway in normally not a problem unless I'm driving 70+ MPH in very high wind conditions.