I've looked into this a bit as I progressively convert my workshop to a studio. Sound "proofing" will be quite expensive, so you should pick your room now. You can get started with a second layer of drywall with offset joints. Fill in the windows (or buy expensive sound proof ones. ...doors, too), locate and treat every crack, crevace and join... Expensive.

Try this: Put a stereo in a room with a door. Turn it on, and close the door. Now crack the door open. Your decible leak just tripled! This is the kind of thing you are up against. Any untreated location (crack, uninsulated joist, etc) will let sound out.

You can get some good results with sound "reduction". Since you need to take your sound'proofing' back down with minimal damage to the structure, you could use 4 x 8 sheets of Sonopan and a half dozen screws to hold it in place. Or cartons of ceiling tile would also work.

It's not sound proof, but I know via SPL decible readings that I can reduce sound leaks by 20% here, 30% there, just with a little attention to the "weakspots". It is an accumulative result. Everything you do helps.

I only know what I have read and happened to have tried myself, so I will also be interested if anyone has any good ideas. Especially for doors, windows, and vents.