Twelve is fine.I drilled my holes on my bin with a 1/4 inch drill bit. You'd probably do well with similar. The holes don't have to be exactly 1/4 inch as it's just what I did. Any similar size hole is fine. Perhaps 10 holes on each long side (not lid) of the tub and see how that works. You might have to do 5 holes on each short side of the lid too, for the sake of making sure you have enough ventilation. Try using solely paper towels in the new bin first and a small handful of damp moss. Don't spray the bin until you see what the humidity ends up being.
0.1 Super pastel