Should work fairly well, I would think you will need to add some additional air flow though.
I am about half way done building a similar enclosure, Ill take some pictures when I am done. The only main difference is that the miners are ported directly outside though a 4" insulated pipe, and the top of the box is closed with a 290 CFM exhaust venting directly outside to keep some air flowing. Its going to be 3'x2'x7' for 2.6 kw of miners.
I am building the walls out of 3/4" wood - 2" Rock Wool Insulation - 3/4" wood - 50 Mill Sound Dampening Material. I am using silicone to fasten everything together so that the sound doesn't travel through.
Sounds like a really well planned solution. Would love to see pictures or sketches of work-in-progress
You are right about the airflow. Additional fans for intake would be added.