Damn, I was in the middle of commenting when
@HorseloverFat - the other Leo, noted that this post dates to 2018, nearly 3 years ago. I'll post my belated comments anyway, as someone else might want to try this species for bonsai. I had a brunfelsia for a year or two back in the day. It did not do well dwelling in the under lights orchid collection. It wanted "more" of something, I assume more light, and or more frequent water than what it got hanging out with the orchids.
so here is my belated reply.
What a lovely, whimsical composition. Nicely done with a species that is not used often for bonsai in the USA. Brunfelsia are in the same subfamily of the Solanaceae as the Petunias. The wood they develop is very brittle, like the wood of herbs such as rosemary. You are correct, in order to shape them you must wire branches before they are 6 months old, or they will be too brittle. This is a delicate process. Good news is, you do not need to leave the wire on very long. Usually less than 6 months, you might be able to remove wire in as little as 12 weeks.
You obviously have good light and near ideal horticultural conditions, as you are getting blooms on a relatively young plant. Getting leaf size to reduce is a problem. Though in this case the leaf size is not bad. If one lived in Florida or other areas where this could be grown outdoors or in a bright greenhouse, it could be a lovely tree.