Soundproofing Condo Basement for Band Practice

I recently moved into a condo with half the basement unfinished. The ceilings are high (the lowest point being 8' to bottom of ducts). The neighboring units are separated by a formed concrete wall. I'm not sure how thick...maybe 10". The rear wall is concrete up to about 3' and wood framed and insulated the rest of the way up. The attached garage is beyond that framed wall. The opposite wall is an interior wood framed wall. The wood framed walls are finished on the other sides, but unfinished on the side I'm interested in using for band practice. The ceiling is unfinished and has lots of space. Above the 12" deep ducts are truss joists supporting the subfloor. It was built seemingly well, around 2003. My ultimate goal is to be able to have band practice (rock music with drums bass and guitars) in my basement without my neighbors hearing us). Given my situation is this possible within a reasonable budget? My plan is to build a room within that room, leaving an inch or two between existing walls. After doing some research, I'm getting some conflicting ideas, but here's my basic plan: 1. 2x4 framed walls 1-2 inches away from existing walls 2. regular fiberglass insulation between studs 3. ceiling supported by new walls only (isolated from existing ceiling 4. 5/8" thick drywall fastened directly to studs (would resilient channel be worth the cost and time if I'm already decoupling the entire wall?) 5. another 5/8" thick layer of drywall with greenglue between. (is the extra layer of drywall really going to do anything substantial for me? What about greenglue? Is there a less expensive alternative to greenglue?) That's my basic plan. The basement is on a concrete slab which is isolated from the walls around the perimeter (there is expansion board where they abut. I'm thinking that will sufficiently isolate the slab from the adjacent units. But would it still be beneficial to use some sort of rubber strip or feet along the sill of the 2x4 walls? As for the flooring, I was just going to use some fairly heavy carpet. Does anyone have any suggestions? Does this seem worth pursuing? I would hate to go through all this trouble only to find that they can still hear us. My biggest concern is the low frequencies. Thanks in advance!