Me...I like larger sized Hackberry trees. I have grounds to grow them out around me. I started a Celtis Sinensis Hackberry 1/4 stick in 2012. That Hackberry trunk at the base is 5.5” diameter today. When I show more Nabari the base should be at least 7”. So....it’s gonna come down to what you like really....Big? Medium? Small?
It appears like you have a good structure started with some complimentary bends. How are the roots? On my trees, I periodically root pruned and brushed soil away while in the ground to push roots in the right directions around the tree....using small stones and popsicle sticks. Making direction corrections where needed. I did my best to create a full circle of roots around the tree...simply because I didn’t know what might be the front while it was growing out and telling me what it wanted to do.
Just for reference.....here’s photos of the Hackberry year 2012 (the stick) and the trunk 2017. It took awhile I think because I kept it, along with others, in a small plastic pot, upsized the pot after one year, upsized again.....and then got smart and put in the ground. It’s ready for trunk chopping this spring. Grew really fast once in the ground. Really fast.