To be clear, are you suggesting I consider layering the top of the new tree?
Not necessarily, but you can. Some people are saying to just prune off the top (and perhaps throw it away) leaving you with a short trunk to use as a base to start your bonsai structure. It is good advice... but you don't have to prune the top when you can just air-layer it off. Just depends on how much time you have and the effort you want to put into it.
As you have found out, if you have good air-layering skills, you can create numerous trees from a single source tree. In fact, many nurseries maintain large trees in landscape solely for the purpose of being able to air-layer off branches for source material.
However getting back to bonsai... a good bonsai always starts with a good root structure at the soil line, a good trunk line, and good taper. In your current tree, you may have created good surface roots with your air-layer, but the trunk doesn't have any character because it is dead straight and has no taper. If you prune it or air-layer it so that the remaining trunk is only 6" tall (or so) you can guide/wire new growth so that you can create an interesting trunk line (anything but dead straight) and good taper.