K_z
Good advice.
Brakes are from one or two manufacturers, no clear winner.
Removable fenders are a must.
Length…..well as the say, size matters. Longer is better. Room to balance the load as well as tie down spares are Important.
Deck. Metal solid deck is preferred, but not budget friendly. Solid wood would be a close second.
Tie downs. An E track system is the most versatile. A track flush with the deck which runs below the tires makes securing the car easy.
Winch. You never know when you need to pull a car on to your trailer.
TPMS is a great idea. If you have a puncture going down the road the only indication you usually have of the problem is when the tire flys apart. 3-5 years on original (read junk) tires is stretching it. Goodyear or Chuck Schwab trailers tires are best.
Tying down an S550 I have found is best done by installing a kit like the ford tie down hooks/loops. They bolt to the body/frame in factory holes. Stay away from straps around the suspension. It’s easy to attach the straps on an open trailer once the car is on the trailer. Not so much with an enclosed trailer.
Watch tire pressures and lug torque specs. Most trailer wheels are not hub centric and rely on the studs to carry the whole load. Too loose or too tight and they will depart the hub. Ask me how I know
Good luck with your search.