Basically without repeating everything everyone's already said, I keep all my animals in bio active and have been experimenting wirh it for about 9 years. If your looking for a commercial mix the ABG mix I've found is your best bet. NE Herpetoculture is a great site and I've used them for several of my smaller builds. However for your purpose and of that size as stated above would be a bag of organic potting soil, without fertilizer or perlite, preferably without mulch. Depending on the humidity levels your going to want to mix in either peat moss and or sphagnum moss. For the separator, generic vinyl screen will work. The main issue I've always had has been the drainage layer. The clay balls can be expensive & heavy. I've been using Matala Mat. Same thing used in pond filters. I've only started using it recently but so far has been promising.