Yes, "after 8" CST SSS won't work. That's a BM answer I know.
Yes and also the SSS is limited to holding over a chord while you change performances. Nothing else fancy is going to happen with SSS especially while on the move. Once I add part 9 to my performance then the "SSS" icon disappears forever.
Read what BM wrote under "SSS". With local control off you can switch between single parts on the fly. I think it's seamless but the touch screen might slow you down so you might want to switch using the actual part buttons. You can go into "Mixing" to see all 1 to 16 parts and try muting/unmuting on the fly to see how it responds. You'll be at the mercy of the touch screen responsiveness in "Mixing" mode.