You should do a build diary!!
Depending on your location, perhaps soundproofing isn't that necessary IE if you're moving out to the sticks where no-one will hear. Sound proofing is where the main cost will come in I think. I've been able to set up a (bit of a dodgy amateur) studio where we rehearse so we can record every practise. I have two sets of drum mics, 4 nice vocal condensors, plenty of dynamics for the cabs, cables, pre-amps, and I can record up to 24 channels into Cubase at a time - all for under £1k. Also, my room is very "live" but i've learned to love the sound of it, although it did take some EQing of the bass amp to stop the ground quaking.