Cleaning after a trunk chop (black locust)

Hey guys,

I have this 3 year old Black Locust Tree(pseudo acacia). It is planted in a big pot with akadama and heavily fertilised.

I have trunk chopped it this May. Now that it is autumn, I aim to clean the would and shape it neatly.

I have proper tools to do so (Japanese saw, concave cutter, etc even a Dremel).
From my knowledge, I should do a diagonal cut.

I want a second opinion though since I haven’t done this before.

PS: The bottom branch, what should I do with that one in winter? Remove it completely (from the trunk’s level) or leave a stub?

Every advice is appreciated, Thank you!