Nice tree! I bought a satsuki with a trunk hollow from Dave this spring at the National Aboretum (Akemi-no-tsuki). I figured it was something a little different from what you see out there in terms of satsukis.
I'm sure you've talked to Dave about this, but he recommended a tree sealant called "Top Jim" or something to that effect.
Its a nice tree with great character but I have to say, it looks like you "cleaned up" a lot of useful foliage. That upper left branch is way out of proportion (it was possibly used as a sacrifice branch to thicken the upper trunk) and seems like some back branches are as well. Looks like you will have to regrow most of the branch structure. Although, I think you should be able to use that big first branch.
Actually i didn't clean up useful foliage. The stuff I took off was less than 1 year old growth. When I cleaned up this tree, I left the main branch structure alone. That is what I was taught. Satsuki bonsai trees should grow out than be cut back in about a three year period. In about three years I will have this tree show ready.
None of the main branch structure was taken off, only the new stuff.
Not think... DEFINITELY!... that branch is key to this tree, nice and thick, beautiful movement. Second branch is key as well. The higher ones its hard to tell from these pics, but I doubt I would cut any of them clean off, probably would reduce that upper left one though.