2-car garage build- important question...

Hi, I'm building a music room in a detached 2-car garage and after reading Rod's book and many posts on this and other forums I decided to rely heavily on green glue. Here's a quick 2D I can go into as much detail about the room as anyone can stomach but for now I have 2 pressing questions... The building has a peaked roof with 20' 2x10 ceiling joists that span the building 9 feet above the concrete slab. There are 6 in-a-row (16" apart) from one wall and 4 more from the other wall with a gap in the middle. I'll be building a wall to create booths under the set of 4 (there is one missing against the garage door wall so the booths will be between 5 and 6 feet deep) and I'll build a 2-leaf ceiling around the joists above it. Q: I'd like to leave the rest of the joists exposed, apply a second layer of 5/8" DW to the peaked roof and wall in the "loft" above the booths for storage. The peak runs perpendicular to the joists so the room is symmetrical other than the joists themselves. Will the exposed joists (edges caulked heavily with "SilenSeal" and surrounded by 2 layers of DW [1/2" - GG - 5/8"]) spoil the sound proofing? Should I add Joists and wall in the entire ceiling creating a flat (almost) 9' ceiling to be safe? Thanks

The other Q (and a bump) is: Is it OK to build the diagonal walls behind the bass traps? I can put small triangular traps in the back of the room (W wall) but the diagonal in the NE corner of the big room serves to make the booth large enough for a drum set and the SE corner I plan to build as a "door" (Masonite or similar hinged on the left) to access the electrical panel behind it. Will the "flat" bass traps work OK? Will the hollow section behind the SE corner create problems? Thanks