John Sayers' Recording Studio Design Forum

Hello.
First of all I'd like to introduce myself.
My name is Wojtek Majewski and me and my wife are currently running a small commercial studio in Windhoek Namibia.
The studio was doing very well couple of years now so we were able to acquire a new property (house) just opposite ours where we are planning to move the whole business to. It is a big erf with swimming pool and lappa for my beloved customers . At the moment the previous owner is still moving out so I'll post pictures as soon as he is gone.
So for the past few months I was researching, trying to source materials in Namibia, a.s.o.
Before I post a plan and concrete questions I still have couple of unanswered questions. I hope I'm posting it in the right sub-forum:
1. It seems that the inner walls of the rooms in the house are mostly double brick walls (10cm*2) which is good and bad.
From my research so far, it is good, because it already gives a nice STC (the bricks are solid, connected with mortar) assuming the walls don't have any cracks and holes. Bad, because I'd like to have windows in them, so matching the density will be crazy (20 cm glass??? ). So the question is, knowing it is going to be the weakest link, can I just use glass thickness suggested in Rod's book?.
2. I cant' seem to find any STC charts with double brick wall on one side and drywall on the other?. Do you have any links?. Thank you
3. Green Glue. I found a place which sells it in South Africa. If I go this route it is going to be very expensive, as Namibia and South Africa don't have friendly customs law.I'll have to pay double VAT (export/import) plus of course a duty, at this time around 30%!!. Question: Better to not use anything between the gypsum boards or find a cheaper substitute, if there is any?. We've got something here. Water based caulk, the manufacturer states it never hardens over the years and has excellent damping properties . Will check the product's home page for more info.

Thank you in advance.

Sincerely
Wojtek

use greenglue its the best. if its too much use resilent channel instead and mount ur drywall to that or add more layers of drywall.