Enjoying your build, some neat ideas.
I like your idea on the tongue and have a possible improvement for you. I did something similar on a log splitter but made the jack part of the fixed (trailer side) rather than the tongue side. It allows me to remove the entire tongue for theft and I'm less apt to gouge my knees when working around it. In your case it would also deter theft and allow you to adjust the tongue without the burden of the tongue weight. It appears you have put a lot of planning into your build so I suspect you may have considered this already.
Best picture I could find, the tongue slides into a receiver like yours near the yellow wires.