Hard to add to the lists of previous posts. But, a couple of things. I'm not much of a purist for LEDs, but at least the sealed, rubber grommet type lights. Easy to find, and to replace, last long time -- and have a socketed lead. The grounds should be treated like all the hot leads and brought up to a sheltered area in the tongue and mounted to a single grounding stud. Grounds are the ban of about every trailer ever made (at some point).
Don't know if this is part of the plan (don't recall seeing it -- my apologies if so): both axles with brakes.
Though it might not be a possibility, I like common spares. Works for my situation, and there are only a couple of stud sizes used in trucks (and probably only one used in trailers, so may not be much choice).
Never wished for a narrower trailer. And glad I wired in back up lights. Presumably you will be requesting the 7 blade round connector?
You will never have enough tie downs. I like the rub rail on the 2 x 4 stake pockets. Get stake pockets on all four ends (or across the beginning of the dove tail). Nice to keep the little things inside with a set of 2 x 12 side boards. I put the triangle shaped steps on the ends of the fenders on one trailer - placed another triangle above it at the bed height to protect my back up lights (back up lights on something that far back are for seeing where the corners are going anyhow). Worked far better than I had hoped. That and using the no slip step tape.
I don't have a solution, but when I redid the floor I had to break/grind off almost all the screws that held the boards down. Wished there was some way to keep them from rusting in place.
My trailer already had a tongue box for stuff. Simple plate welded between the rails, with a front and rear filler in the vertical and a hinged lid on top (used a long U bolt welded to the frame sticking up through a slot cut in the lid for a locking point).
How about a 12v cigarette lighter output on the tongue? Drop light, etc.
