Oh, Nice Jacarandá!
Congratulations on getting this far with the sapling.
Here in Brazilian winter they'll loose it's leaves, and flourish on spring even before showing new buds, so it takes a little time on spring to it to backbud, for what I see, you should maybe work a movement on the trunk while it still flexible, just make sure to not make it tight, as it grows fast... I would soon put it on a bigger training pot...
About pruning Jacarandás it's never a easy topic, I've heard from experienced guys that if you prune it too much, you can stagnate it's growth, but I lack of knowlodge to second that... So I think (for what I've seen with my friends) you prune them once a year, on spring/summer... That being said, I would wire it and let it's apex grow to thicken the trunk.
Maybe some Jacarandá owners can give you better insight, I only have a few young ones. They are wonderfull trees.
