Aaron,
There's a very nice, extremely detailed article in Bonsai Today #39 about developing a maple from a similar position as yours (trunk finished, time to heal scars and set primary branching).
http://www.stonelantern.com/bonsaitoday1995.html#
If you can get a hold of this issue by hook or by crook, it'd serve you well.
(Your tree looks like a better piece of material than the one in the article.)
-Carl