Practice Studio/recording studio in NYC co-op

Hi there, I just found this forum and I've spent most of the afternoon reading various posts. I'm a jazz drummer and my wife is an opera singer. We're looking at buying our first apartment. The unit we've found, and made an accepted offer on, is on the 5th floor of the building. We'd like to soundproof the front room for practicing and recording in (about 350 sq. ft), without bothering our neighbors. I've been in contact with a couple of firms here in NYC, City Soundproofing and Acoustilog. City Soundproofing says they can do it for around 30k; I'm waiting to talk to a consultant from Acoustilog to hear what he has to say about the feasability of such a task. Basically, I'm wondering what you all think of my undertaking this project....is it going to work, can it work? It's a really old building (1937 construction) very thick walls and ceilings...I've been there 3 times at different times of the day and I've yet to hear anything from their neighbors. City Soundproofing suggested building floating floors and making the room within a room design. I'd just hate to do this and then have my neighbors complain about the music. What do you think? Is it possible? [removed]