Years ago I designed and built studios for a radio station we had. Besides sound absorbing foam on some walls and in corners I had a double wall (off-set 2 by 4s for each wall on a 2 by 6 plate), that the studios shared, with insulation in it. Most of that just doesn't seem to practical for your garage, but even shag carpet on the walls (70s style) would help. Poultry dust will always be a problem and a building separate from the house would be best.
The indoor breeding units I built are pretty much what I would recommend. The difference being mine are/were just for the breeding season and prepping birds for the show season. For housing birds year round I would make some holes wider and taller if you have room and only have one row, so you don't have to bend over. I would not go deeper than 2', since that is too far to reach in to catch birds, collect eggs and clean the coops. Note the roosts in my 12 hole bantam units. I would make the LF coops a bit higher, so similar roosts could be added. Maybe only have 3 holes across, instead of 6 for the bantams. The LF coops are wide enough for individual hens and visiting cocks. They are also idea for pairs and trios of bantams.
You can find many photos and details about these and other coops by doing searches on this forum. If you want more photos, just ask and I'll see what I can find.