Here's one thing to consider if you are willing to draw this out a few years. I like to play with maple nursery material as well. When I get a young tree that I know is too lanky for a single bonsai, or that is grafted and needs to be moved to its own roots, I will wire all branches that I can successfully bend and treat each branch as a future air layer a few years down the road. Once a branch gets too thick there isn't much you can do with it if it doesn't already have movement. So best to add movement to anything you can now, while you can, and then find fun pieces to air layer off later. That assumes you enjoy the challenge of air layering, etc. Not for everyone.
Here's a simple example from this fall. I picked up a small acer palmatum cultivar with long, straight growth, and a graft. I just wired up random movement wherever it was possible. No plan really. I'll then let it flush out, remove the wire, and repeat each year for a few years. During each repeat cycle I'll start to think above design for each future layer: remove bar branches, coordinate branch movement, etc. After a few iterations you'll be able to air layer off side branches, the apex, and so on with enough movement to make a few good trees from your original material. And they'll all get there pretty fast because they'll be doing that growth on the larger rootstock of your 6 foot tree.
Small nursery palmatum. Maybe 5 feet tall. Not a lot going on here that looks like a bonsai:
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After wiring for random movement. See that I couldn't bend the lower and middle trunk, since it was already too stiff. So I just ignored it and won't use in any future air layers.
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End result of this process after a few years. This is a different layer from this Fall, but is basically air layering off the lower left branch above a few years from now. That is in a 10" wide pond basket for context:
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Good luck with your project.
