almost new construction questions

[mharr552000]

I met this guy who has a property he is marginally interested in selling. It is a 5 acre lot on a road with 9 other 5 acre lots. He is living in a small trailer on the property, but he has constructed a 4 car garage and a 40'x28' cinder block out building(his future wood shop) with concrete floor, 10' walls, open rafters, a 36" steel door, an 8' over head door, rough in 120/220 service and rough in plumbing.
This outbuilding seems like it would make a kick ass rehearsal/recording space. Currently, sound isolation isn't an issue, but as the other lots get sold it might be. The building is about 200' from the property line.
The place is just a shell now, but what kinds of stuff would need to be done to it to keep from pissing off any future neighbors? Removing and blocking over the overhead door opening as well as bricking the exterior(it is set up for bricks) seem like good ideas. How about filling in the cinder blocks? The extra weight could potentially crush the foundation, no?
My wife said she wanted a few acres. Our current lot is 0.168 acres! Hmmm...$180,000 for a lot with no house on it will be a tough sell. All five of us could live in the studio. Just fasion rooms out of gobos!

[Innovations]

Your biggest friend is the distance. 220 feet is a lot of separation. That being said filling the empty cells of the block either with cement or sand will not crush a well built foundation.

Before you go crazy on the walls though what is the construction of the ceiling and roof? An outbuilding intended as a wood shop might just have a tin roof over rafters. Sound always travels by the path of least resistance. So what is the ceiling and roof?

In all cases what you are looking for is a mass-air-mass combination. So for the walls you can either build a separate inner set of studs with an inner layer or two of drywall for the best, but you would also likely be able to do with resillient channel and an inner pair of layers of drywall. Remember that the airspace should be filled with something like fluffy fiberglass so that it does not itself become a resonating space.