Thanks all for the advice---I really appreciate it. I'm now leaning
towards a subpanel in the studio, as running 6-8 circuits from the
basement to the 2nd floor attic is going to be difficult. I have a
passage that will work for 2 or 3 cables, but 6-8 will require a lot
more fishing.

I appreciate the 12/3 cable idea...I'll consider that. This would
also be easier to accomplish with a subpanel (so I wouldnt' have to
move current breakers to get on both sides of the incoming).

Just to clarify--when I originally proposed 30A outlets I was hoping
that 30A outlets were available in the 'normal' blade style (e.g. it
would look just like a 20A plug but would allow up to 30A to be drawn
through it, say for two griddles). Clearly that's not the case.

thanks again