I just purchased a Northern Glow Maple (Korean/Japanese maple hybrid) for a landscape tree (though it may end up as a bonsai) and it needs some structural pruning. I am planning on doing multiple air layers this Spring (after the leaves harden) on the areas where there are 3-5 branches originating from the same places (leaving just 2 branches).

Above this section the shoots extend for 3 feet with basically no branching. Instead of just clipping these back to create branching lower I would like to also collect material for propagation.

What is the best method to use here? More air layers or take cuttings? Has anyone had success with propagating from hard wood cuttings? What was your method? (Should I take 6" cuttings this Spring, plant them in pumice and keep them inside with a humidity tent?)
I'm sorry this is late, but I'm also in the air layer camp. I think you get better rooting, and the tree is able to keep feeding water up to the branch so there's no need for extra humidity, and less worry about mold.
I took my first successful maple air layer last year, so I'm quite new at this. Take all of my suggestions with a grain of salt.. lol.
I have tried and failed at hardwood cuttings of deciduous. I would probably do what you plan and do some air layering. I have had more success with that. It is not something I do a lot of so I can't claim expertise.