Building a stereo room and ran into some problems, help!

I am in the process of building a dedicated sound room and have a couple of situations that have arisen that I cant find a suitable solution to (within threads of through google searches) so I am seeking advice here... background details:
1. Of course I want absolutely 0 sound transfer but I realize that isn’t possible as I haven’t won powerball as of this typing.. So, my goal is to let as little sound out of the room as possible (particularly bass) so as not to bother my wife and kids (that are either one floor above during waking hours or two floors above late night) or the neighbors whose walls are about 20-25 feet away... on a tight budget of course... Obviously I also want qualty sound inside but first things first...

2. The room is in the basement and I went with the "room-within-a-room" motif as the walls are about 3-6 inches from the actual walls, the ceiling is about 18 inches or so below the subfloor above. There is a crawl space below the basement floor so the floor is plywood, not concrete. The room is 11x15 with a 7 foot ceiling (low, but there’s a lot of duct work and piping so it was easier this way..)

3. Sound proofing/isolation: I floated the framing on top of some styrofoam I saw while buying the lumber.. From what I have read styrofoam isn’t the best sound proofing material but having something between the 2x4s and the actual floor sounded logical so I went for it in an effort to keep the crawl space from acting like a giant drum... At worst, I took a chance and blew 15 bucks... There are concrete walls surrounding about 1/2 the room and they are insulated, the rest of the interior area is pretty much open (walkout basement so the front 1/2 is underground sloping down so the back 1/2 is above ground..). There will be insulation between the studs (R13 I believe) and two layers of higher R rating (attic level stuff if memory serves...) in a crossing pattern between the "ceiling" of the room and the subfloor of the floor above. The walls will be 2x drywall with green glue in between the layers with regular drywall on the backside (outside of the room facing the rest of the basement.) Obviously will be sealing the gaps between the sheets of drywall, between the drywall and floor, around outlets, etc... Two cases of green glue have already been purchased...

3. On the table... as with most construction budgets, what you think it will cost and what it actually costs are two completely different things... So just like everyone else, money exists but supplies are diminishing.... I’m looking for effective and as affordable as possible...

The questions:
1. I am considering using the aforementioned styrofoam as a buffer between the studs and drywall.. adding the styrofoam means three layers of "wall" (styrofoam, drywall, green glue, drywall) on the room side of the studs. Thoughts?

2. I don’t plan on finishing the drywall so am curious about how to "finish" the walls and have the makings of a good sound space and also contain sound as much as possible...this is a dedicated room so functionality is the important part... My original intent was to put industrial carpet on the walls and call it good (then add panels as necessary)... I am also considering curtains or large panels that are similar to moving blankets but made specifically for the purpose of absorbing sound... The curtains I am seeing are marketed as black out curtains but the sound isolation benefits are mentioned.. and it’s relatively cheap... I doubt their sound absorption capabilities are "all that" but it is an option... Thoughts or other recommendations?

3. The ceiling... In theory I was/am going to do the 2 layers of drywall and green glue here as well... Ran into logistics as that gets REALLY heavy really fast... So, out went the 2x4s and in came the 2x6s... So now that I have the capability; considering I already have (from high to low) subfloor above, about six inches of open air between the joists, the two thick layers of insulation, and at least 1 layer of drywall.. is the double drywall and green glue necessary?
3a. All of the web sites have begun to blur together but I believe I saw information that stated 2x6s can hold the weight of the two layers of drywall

4. I need to get air in and out of the room, without negating all the aforementioned efforts.... I am blocking off the air vent (physically stuffing the vent with a blanket and not connecting it to the room at all as it is above the ceiling) that would go to the room in an effort to not funnel sound directly to the rest of the house.... So far, I have come up with something along the lines of flexible tubing (dryer vents?) with baffling similar to a muffler inside to simply circulate the air from the basement in and the room air out... this isn’t even an educated guess as I have no background knowledge whatsoever... obviously any thoughts on this would be greatly appreciated as I have found no information anywhere on this issue...

5. The drywall itself... Pretty much everything I have read has stated that 5/8 drywall is far superior to 1/2 inch and one would be a fool not to use it... However, the research presented on the green glue website pretty much contradicts this as the thickness of the drywall had no impact in the final rating (I believe the acronym is SRA). Thoughts?

Any thoughts on on these ideas would be greatly appreciated!!! Also open to suggestions as well but at this point cost is becoming more and more of a factor as I am pretty much already 2x the intended budget so please keep that in mind...

thanks!