A few more tips for your consideration:
If you really want a tree at 12" tall, you really need to be making the cut at around 8" then growing a leader from the top of the chop. This leader is then grown out until its around 2/3 of the trunk thickness at the chopsite. Then its chopped again anywhere from an inch to 3 inches above the original chop, then grow another leader and repeat. This build really nice taper all the way to the top. In the meantime you can also build the branches, lower branches should be left to grow till they are again 2/3 of the desired thickness before working on ramification.
All this apex/branch building requires fast growth and would be better in a larger grow pot. But the current pot isn't too bad.
You can probably fill in the bare area using thread grafts see
here , another use for those grown out branches
I find it best to hold off pot selection until the tree is almost show ready, as trees very rarely end up exactly as envisioned.
Hope that was of some help.