First thing I would do is reduce the cut scar to live bark, trim and reseal all around. In the current state, the scar will never heal. Make sure the new cut is concave, and not a flat V, with a margin of live bark all the way around.
If you plan on keeping those branch nubs, I would also recut them with a concave cutter and seal them. They look right now like they were cut with a saw - that torn edge should look instead like it was cut with a razor. Make all your concave cuts face upwards so that you can hopefully get buds that will grow outwards, as well as towards the front and rear - instead of straight up and straight down. From this point forward wire all your new growth the second it hardens from soft green to wood. Do not let the growth run 6" without wiring it. Even a 2" segment that isn't wired becomes trash and will have no future in the design of your tree.
And the big elephant in the room... what does the nebari look like? Make sure you understand your roots before you design the top of your tree. Never design the top of your tree first, and then work your way down the trunk. Always start at the bottom and work up. In a perfect world, you would have made that v cut based on what your roots look like - because the v is going to define the front of your tree. It's all good though because elms are so indestructible and you can easily fix root problems; but keep it in mind when you work on other material that is perhaps less forgiving.