Garage conversion, 29.5 x 29.5...help!

Hello! This site is great, I've been lurking for a short while and I think I'm ready to convert my garage to a studio with multiple rooms. What I have is a 29.5' x 29.5' interior, excellent condition concrete floor, 9' ceilings, and a stairwell heading up to a finished room over. The a/c unit is located in an attic above the garage, but there are two vents currently poking down into the garage area. The intake however is upstairs in the loft room. I figure the upstairs vents will be detached to dedicate the HVAC system solely to the studio, and I will use window / area units upstairs for the rare occassion it's occupied. There is a 5" beam running across the ceiling, a garage door that I plan on removing and closing in, and several windows that I plan on removing as well. There is also a decorative brick structure 12" tall that runs around the interior of the room walls with a 2x4 painted sitting atop that. What I'm looking for is a control room, large studio space, and a smaller room that could double as a drum booth or hold loud amps. The stairwell area is pretty much a must as it allows people to enter the back door and not have access to the studio but allow them upstairs to the loft. I am attaching eyeball drawn pics that aren't exact, but represent rough dimensions that I would like to see acheived. I really have no clue where to start with this, I'm having a friend come down soon who owns a construction company and want to be prepared with things to ask for. My budget is $15,000 to $25,000 maximum. Obviously, I'd like to do it for $5k if possible! I live in the country and my neighbors don't complain in my untreated loft space when I play drums and record at night. I don't need isolation like a gun practice range, but I want good separation, quiet air system, etc. Any advice appreciated. I searched and searched but couldn't find anyone with near my dimensions etc. War PS: The space dedicated for the stairs doesn't actually exist, it's in both pictures though as I want to keep this space only for loft entrance.

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That layout looks ok so far. Does your heating/AC system have any return air? There are sticky threads somewhere around here talking about how to protect air ducts, so you should have all the data you need on that stuff.

Yes, the intake is upstairs. War