you frame is super heavy looking. Be careful not to build it too much.
I also agree the sides at 24 are plenty. But even 20 is good. Think about the height of a cooler etc and how it might be to reach inside for that. 30 is too high. At that height everything will have to be accessed from the back.
I've seen lots of trailers(homebuilts) made out of serious box steel and are just basically over done. Then the springs and axle are just regular.
But your springs and axles might be absolutely fine for a trailer that is pulled by a cruiser. There is absolutely no need to build a 4x7 or smaller 3 ton trailer...
