I was hoping someone would "weigh" in on this subject. I don't want it to be too heavy, but I still want there to be enough structure for sustain. Right now I think I've got it at close to 1" around the perimeter and about 3/8" thickness at the bottom of the cavities. Is there a rule of thumb as far as how much material thickness to leave? 1/2 inch, 1/4 inch?
I'm also planning to rout matching shallow cavities into the topwood before I glue that on. Any other suggestions are greatly appreciated.
I wouldnt worry about sustain. so long as it is a strong-rigid structure with no movement in the neck you should be fine. Mass does not always equal sustain, look at olah strandbergs guitars, tiny little things but they sustain like a Les paul.
Personally I route out a hell of a lot more than you have here & still have no problems with tone or sustain. Id leave plenty of meat in the bottom guitar for balance, But the top can be hollowed almost completly out. Just leav enough anchorage for your bridge.