Reasonable solution to building room around iso booth

Hi folks. I have read countless threads on this forum and understand that this question will be met with many ideas and or concerns. So here it goes... The Background... I have a modest recording set up in the basement of my home. I had decided to purchase a large vocal booth, 8'x10' in exchange for building a live room. I paid a 10th of the price of a new one of this size which at the time made sense verses the cost and energy to build a "proper" live space in a basement (if there is such a thing...I am a realist) The booth is excellent in many regards and has greatly improved the quality of vocal recordings and even drums have turned out quite nice. However, the isolation of typical airborne noise such as the HVAC unit (only three feet away), floor borne noise above (hardwood on Kitchen floor), and bleed of control room monitors back into the mics in the room does exist in the recordings. It isn't terrible, but it is not dead quiet either. For the most part it has never ruined a good performance or hasn't been worked around, but the fact that I have to monitor lower than I would prefer and have to turn off the AC in the home during vocal recording is just a pain. I have 18" of clearance all the way around the booth and only three inches from the ceiling of the booth to the open joists above (joists have typical plumbing and HVAC duct running through them). I want to insulate the ceiling and build a wall all the way around the booth, insulated. One wall will touch a concrete wall and the others will have another 18"+ of space beyond. So in essence imagine a 20'x14' concrete wall typical basement, with approx. a 12'x12' framed wall (the one I will build), with a 8'x10' vocal booth inside. A room in a room in a room. The help I need... I am looking to reduce noise transmission. I will defuse and bass trap with readily made off the shelf products. I only want to reduce noise through the floor and walls. Based on my readings I have come to understand that the quality of the results are in the fine details. However, considering my budget I want to focus on the materials and methods that will give me the biggest bang for the buck. 1. Will Roxul insulation be the right choice or will a typical Owings Corning Pink "acoustical" insulation from Home Depot be as good? 2. Is my comprehension correct that I should not buy insulation with the brown paper on it because the paper creates another "leaf" 3. I should only use drywall on one side of the stud correct?...because drywall on the second side creates a second "leaf" that would decrease the results, correct? 4. Would two layers of drywall with small cork spacers between really cut down on transmission or would the additional layer provide minimal results considering I am cutting so many corners on this project anyway? On many gear forums I always get a kick out of those who post questions like...I have a 99 dollar budget for a mic...which one should I purchase that will make my vocals sound like a hit record? I understand that my post here is much like saying "Hey all you pros out there...How do I make my studio have acoustic qualities of the best studios for less than a 2000 dollars?" Its almost laughable...but I still need to ask. As said...any tips that will give me the best bang for the buck would be great. Thanks, Ross Hancock Baltimore, MD.