I just make all this up as I go along. (Can you tell?) I do have a very nice Vantly cargo trailer, rated to carry 100 pounds, which is more than enough for what I do here in suburbia. I have worked on MUCH larger bike trailers with self-acutating brakes, but it's easy to get to a point of diminishing returns with these things: You can load the big ones so full you ain't goin' nowheres. ESPECIALLY up hill.
If you are looking for an around-town cargo bike system, look at adult trikes (NO, I'M NOT JOKING) and those Way Cool Dutch wheelbarrow bikes. I built my own cargo trike out of an old Schwinn Typhoon cantilever frame and a Maimi Sun trike rear end. I built a cool wood stake-bed cargo body for the back with a tail gate- and cup holders in the tail gate! It's a hoot. I also made it a fixed gear trike so I have reverse. I like that, both for the reverse and the ability to apply a mild braking force to the rear axle through the pedals. (Mighty tough to do "nosies", though.)
My wife, by the way, has a very serious Worksman Mover industrial trike. Just the thing for moving major appliances. Again: Not a joke.