I gave it a post hardening prune and the new growth is over a foot long already. I wired the leader again a couple weeks ago and the wire already looks like it is starting to bite so I don’t think I need to worry about thickening up.
Update: I was more organised this year and managed to get this Hornbeam boxed up. This was the first repot after collection so took a lot of field soil out of the root ball. Also had to chop some really thick roots that were preventing me from putting the tree deep enough in the box.
Final pic is what Ryan recommended vs where the tree is now.
Time to let this go mad again for the year. Fingers crossed it’ll push out 2ft long branches like every year so far. I plan to guy wire the first major branch on the right in the final pic down to give the up and out aesthetic. Stump at top still needs to be dealt with, any advice there is welcome!