Thanks mate. Yes - I plan to engage a professional and just pay for advice upfront, but not many people know taiko in this part of the world. Bass traps already planned. we already practice with earplugs and I'll do my best to make it comfortable for the students, but the real worry is investing the money and then getting shut down because of external noise.
A builder has shown me a hollow wooden wall filled with pebbles (about 10" thick). Another guy has shown me a similar sandwich type construction with a third zigzagged wall in the middle and the spaces between the angles filled with a hemp like insulator. Unfortunately for them, it's all guesswork.
I'll keep looking and talking to people but I appreciate your replying - thank you.
"A closed mouth gathers no feet"