We have a number of small Crabs from forest to singles. These do heal ok while young. I have all in Boon mix now. I feed them lots, osmocote and every two weeks fullbore + miracle gro with humic acid etc, water when drying out and give them at least 1/2 to more sun as long as it isn’t blazing hot. Where I live it rarely gets above 85 so mine get full sun.
They grow fast, so watch them if you wire a branch and expect to keep it, as they scar easy.
As far as cutting goes, if it were me, I‘d chop to leave a stub above the first branch myself at 45 degrees to start some directionality and let her run from there.
Also, it would’ve been good to work it’s roots before the repot, but no worries, do it next spring. That will give you time to study the threads here on the Ebihara method and read up on styling progressions for crabapples and their ilk. Remember roots first!