Great advice from Joen..
Just a few "general pointers" around your questions:
"What should i trim"- as Joen pointed out, trimming the stuff you want to stay small is important. If you want thicker trunks, you have to let them grow... if branching is your goal, prune as many times as you can in a growing season- prune, let it grow out, prune back to one none beyond the original cut, let it grow, rinse repeat...
"Should I rearrange"- YES. Again, good points from Joen, a few more- smaller trees in the back and on the edges generally for perspective. Do not make them all exactly the same height- usually your larger trees will be bigger (shocking stuff right?). Some people tend to make the smaller ones on the endives flair outward a bit more, and that to me is a cool look, but this is your forest! The suggestion to add more trees is a good one potentially but completely optional. When rearranging, I assume you will eventually move a shallow wider pot?