Way to many issues to address in a short forum post. Especially with very little info on the future building plan. But heres a few for starters, although each have many other issues and solutions.
First off, my disclaimer. I certainly do NOT claim to be an expert on any studio related subjects.. However, there is a member here who IS. Rod Gervais . Buy his book...HOME STUDIOS..BUILD IT LIKE A PRO
You will learn more than you could possibly EVER learn from forums.
But here are a few of my own considerations.
As far as isolating the basement from the rest of the house and neighbors. Since you would like to record full ensembles(4 or 5 musicians), this implys a high SPL rockband. Therefore, for isolation, it requires the best TL(Transmission Loss) you can afford. However, high TL requires decoupled mass which translates into WEIGHT, detail insight, and depending on goal, a hefty budget as well.
Hence...
1. Have the floor above the basement ENGINEERED to carry a MASS load equivilent to your intended Transmission Loss target. Pre specify flooring products for rooms above to be installed over decoupling pad products for foot traffic noise reduction. Also specify sub floor products with heavier than normal mass. Possibly two layers 3/4 MDF or combinations such as drywall, plywood/MDF..or if budget/code restrictions allow, even a 2 or 3" concrete overlay. Remember, low frequency Transmission Loss is Mass/decoupling dependent. See below for recommended second leaf(basement ceiling) of this assembly.
2. Make sure the contractor guarantees the SEAL on the basement below grade foundation/slab, regardless of what scenario is used(see below)
3. Plan on one of the following TWO HVAC scenarios.
a. A completely seperate HVAC system for the basement. Specify Low velocity, high volume delivery(large ducts) and noisless registers/grills for basement areas. Locate indoor mechanicals in seperate closet decoupled from structural elements and sheithed as per TL requirements. Locate exterior mechanicals on thick concrete pads with decoupling elements. Use resiliant decoupling connectors for plenum to duct connections and isolators for rigid duct work. Use interior LINED duct everywhere with a layer of insulation on duct exterior. Normally, studio HVAC systems are designed via an NCR noise curve rating. I suggest you investigate.
Note. Typically, home studio HVAC registers PENETRATE the interior shell. Try to eliminate this by building soffited ductwork WITHIN the basement iso shell.
b. should you use ONE system for both the basement and rooms above, have the ducting system for rooms above engineered in such a way that the basement ducting is seperated via a baffled plenum, and where possible, ducts to the rooms above and basement be installed in joist cavities unless a dropped ceiling is used. Also, where possible for the basement utilize duct paths with at least two 90 degree bends. Possibly use inline baffeled silencers.
Also, plan on a built in de-humidifyer as part of system.
Plan on as high as ceiling as possible, even 10-12 feet. This will allow a decoupled drop ceiling load via RSIC clips/hatchannel supporting two or more layers of drywall. Planning on this in the beginning will allow other benifits such as a splayed ceiling in the CR and thick absorption/diffusion ceiling panels in both CR and Live room if space allows. Also note this. HVAC ducting in Home studios typically PENETRATE the interior shell. Having a high ceiling will allow for building a SOFFITED ductwork within the iso interior shell, thereby eliinating one big iso headache.
4. Specify the Stairwell as a Soundlock, with heavy duty door jambs and solid core doors with DOUBLE seals at both the top and bottom of the stairwell. Enclose the stairwell and shieth with drywall as per TL requirements...ie...establish TL target within budgetary and phyisical construction constraints.
Note..Typcally, a rock drummer can produce 110dba LOW FREQUENCY sounds. Financially speaking and known physics restraints suggest Transmission loss goals to completely isolate these sounds is next to IMPOSSIBLE. Do NOT think you can ever achieve this ie..100db iso at 40 hz or below..unless you have VERY DEEP POCKETS and your local Building codes allow for it.
(do a search on Galaxy Studios for a lesson in high TL engineering enlightenment
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5. As far as interior basement construction is concerned, plan on one of various scenarios.
Room within a room construction.
a. If more than one room .. Specify ISOLATED slabs with each room perimeter wall foundation footings seperated from building shell footings. Specify sealed expansion joints products.
b. If single room...see a.
c. For ceiling, either suspend multi layer drywall ceiling from Iso clips/hatchannel hung from engineered joist system, or build seperate joist system supported by interior shell walls. Although, this takes more height away from available basement room height.
Econo iso construction..meaning NO decoupled slab.
a. Use decoupling pad products to isolate interior partition wall floor plates from slab, and decoupling sway products at top plate or studs.
b. Or for perimeter walls, use furring and decoupling products such as Resiliant Channel or RSIC clip/channel type products to decouple multi layer drywall from exterior concrete perimeter walls.
c. PRE sheith floor joist cavity above with 2 layers of caulked drywall. Use Resiliant channel for decoupling econo ceiling. Address all flanking paths within joist cavities. Especially at partition wall between two basement rooms.
d. If possible, specify an isolated slab area for drums, possibly 10" or 12" thick. Specify sealed expansion joints. OR, form up a "floating" concrete drum riser. Possibly use a KIP or similar product to decouple riser from floor slab.
Well, thats all I have time for at the moment. There are tons more issues/options to address so read Rods book. As one acoustics guru puts it..."good studio building is 90% design/planning...10% construction." I used to argue that statement. Accepting enlightenment isn't easy sometimes. Till you fail. Unfortunately, hindsight in studio building isn't cheap. Nor possible sometimes.
), over the last 15 or so years, whenever I visit friends' new houses or flats, or many of the offices or warehouses that I deliver stuff to, I often imagine which part I'd turn into a studio and how I'd do it. It's great fun and like with 816 matt, I'm excited for you. Whatever you end up doing, have great fun doing it, whatever frustrations may rear their heads along the way. If your excitement can be communicated to your wife, all the better. 
