Glass is definitely the way to go and its super cheap. I tried plexiglass. It warped in less than a month lol

As for the tank size, a pair to a trio would be just fine. Its honestly all about the landscape. They need lots of hides and climbs. Lots of ups and downs. I recommend LOTs of plants. It makes them feel much more secure. Once your tank is built, you could post some pictures so we can all drool =)