High roots very quickly thicken the trunk at that point so when you decide to cut off later you find inverse taper below the root junction. In addition, after removing roots or branches the tree tends to put on extra growth in that area = extra thickening = more inverse taper. After experiencing these problems I always eliminate unwanted root as soon as possible.
One of the features of traditional broom is really good nebari. That will mean getting the roots right from the start. I'd be removing all 3? of those high roots asap. If you just cut the roots and leave the ends in the ground most will produce buds and start growing. You'll have 3 new Chinese elms to play with by the end of summer.
Planning style while you have a tree fast growing seems to be a waste of time. I started out that way but found that the trunk and branches change so much in just a single growing season the plan no longer fits the new tree. Your tree is likely to go through a number of stages as you grow and chop so what you see now is probably nothing like you'll have in a few years.
More productive to grow the tree to approximate size then work with what you have at that stage.
Need to be aware that ground growing increases trunk thickening. Unfortunately it also seems to increase any faults like inverse taper, swelling, etc. Try to stay on top of things like excess branches, runaway root, etc.
I don't see any location on your profile but guessing somewhere in Southern hemisphere given the tree is in leaf now? Your location will have some implications on what you can achieve and when to implement some techniques. You will usually get much more precise advice if we can see your location. Adding it to your profile saves having to remember to type it each time you post.
