Nice start on your trident. I have been enjoying watching my tree get naked as well. November 3rd, and still not quite there yet.
I am not an expert, but assuming the first photo is the front, you could let the trunk thicken more for 2-5 years in the grow box it is currently in. Then, chop just above that first branch on the right and train that branch as the new leader. Again assuming this first photo as the front, I would remove that branch low on the trunk that is coming straight at the viewer.
In my opinion, as deciduous material for bonsai goes, Acer buergerianum is the overall best in the world (of any species that is widely known in cultivation at least).