I would say around 10-15 but be careful that they don't start nibbling on each other. It doesn't matter how many in a cage if you don't feed them enough they will start to nibble on each other.
I would make a hole in the top and attach wire mesh in side. I would get the 4 pack of those cages so I could separate any trouble makers. I would also cover the sides with paper so that they can't see out.
Buy 21x15x8 solid rubbermade totes and keep about 5 a bin, better and cheaper than these.
BTW whats with the holes? You do know you will need basking and uvb lights for each right?