Hi baron,
I am thinking of trying to find the best way to answer your questions, so here goes.
If you do all those air layers my concern would be for the health of the tree going forward. The red bark maples are not as strong as the regular JM’s for both growth and roots.
Chop maybe too low to start with, and yes a compromise is called for re the bottom two trunks/branches. Scars versus lots of growth, but you will get lots of growth from the top of the tree if you don’t prune and select one leader to go for it. So,you could air-layer side trunks, you could use the bottom branch as new trunk line, and lastly you could buy another maple ( regular green leaf JM) etc to practice with.
Lots of coulds here lol. So a bit of theory for you - every where on the main trunk or branches you see a pale line that goes all the way round ( sorry no computer to paint) are POTENTIAL bud out areas. But you need the tree to grow vigorously before chopping to get it to bud out so to speak. Also remember (if you didn’t know) that most trees are apically dominant so the growth at the top of the tree is the strongest. Great for growing trunks but not so easy to ramify lower branches once your tree has the 3 plus trunk sections.
See
@markyscott ’s threads on trident growing - 2 to 3 metres of top growth uncontrolled (no pruning).
Maybe this photo might help the explanations ( my practice chop to prove to myself the tree would grow lol). I will take a photo tomorrow for you of this tree’s growth as my season’s growth just finishing.
View attachment 186423View attachment 186424
So two regular JM’s as you can see on the left photo where the buds are popping and the lines etc.
Anyway, my problem half is that I don’t want to tell you what to do, as you will experience this stuff first hand and learn way more than advice from others.
Happy to chat, and hope the confusion is vaguely answered?
Charles