Hi Bill,
I kinda like this tree! To me it is in a rough state and needs to have some key decisions made soon....
First the roots...... It will take a lifetime for Will's idea of them bulking up unless you put it in the ground where it would take 5 yrs for anything very noticable to happen. That runs its own risk of death... in the ground Korean Hornbeam are touchy. They like to throw suckers and that will kill the main tree very fast. They also don't like to have roots cut hard from the ground and 40% of trees die during this stage. It is the nature of the beast. If it were my tree I, and knowing you are dealing with 1 tree and not 100's, I would plant it in a shallow but wide grow box and let it go for 5 years or so. Most important part of this will be soil. Try your hardest to find volcanic pumice, nothing grows fine feeder roots and promotes root growth like pumice. A mix of pumice and 30% sifted bark dust will send this tree into a growing frenzie!
Taper..... the taper issue doesn't bother me so much, but since it is decidous and normally best viewed in the winter time it does need to be corrected. Again if it were my tree, I would chop it and plant it in the grow box as mentioned above all at the same time. With a heavy pumice mix you will see very happy, healthy growth in the whole tree and should be able accomplish all the things to make this a very good tree in a short period of time.
That one branch either needs to go, or wire it and bend it giving it some movement to eliminate that straight section.
Pot, ahh...don't worry about a pot now, you have lots of time for that. It seems to be in a terra-cotta container now doesn't it?
There is my 2cents worth, and really you have an excellent start here!
Dorothy's 2nd virt is pretty nice!