First, love this tree, love to have it in the garden! I'm a bit biased, I like BRT's , but this one has great shape. I think you did nicely, from reading your write-up, in removing some heavier growth. Crown looks open and probably more "settled" than a "before" shot would have shown.
The more "congested" areas on the lower branches is good for their vigor. Your MH lights may penetrate the canopy better than less powerful set-ups? Have a large one on the ranch under "higher-end" lighting, works well but has made the crown too vigorous to the detriment of the lowest branches that receive that much less light. So maybe watch for any signs of reduced vigor in the lower structure?
I see where Bill V's mind was going with the small pot. In my experience, BRT's will still grow pretty vigorously while pot-bound. The trunk, however, will take some time to "thicken" with this approach. Maybe you can gradually "step-up" the container size to kind of have some idea of how much the trunk will thicken compared to your image of the tree in the future? It has a delicate feel and flow now, a wider, shallower pot, allowing the roots to run and warm in the sun might swell the trunk a bit too quickly. Well, as much sun as we get in our northern climate.
Usually repot mid-late May here. Instead of a tray of water, perhaps submerge this smaller pot into a larger one filled with soil? Even a large, well-moistened container won't stave off the "reflexive" action of the leaflets in full sun exposure/ 90+ degrees heat with low-ish humidity. But yes, that's a REAL small pot.
Again, nice tree,
@coh these are real fun, as you mentioned. A bit of Bill V. provenance is swell too. Material this size with fair shape is getting harder to come by "up north", in conversation with Michael of Bonsai West this past weekend. He does have a ton of what appear to be rooted cuttings on offer.....'gotta keep the lights on and the water flowing!!
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