Ditto on what the others say. I agree with Vaughn on their growing faster with crickets, but they will eat and grow and be healthy on just the CGD. Anything from a ten-gallon on end on up will work for one adult crestie, but if you give them more height they will use it. I really like the plastic wall cabinet enclosure I made (see a photo in the caresheet) because it has plenty of height and space and looks less like a Rubbermaid in my living room, but it's still easy to clean and to move. It's been my experience that cresties do seem to appreciate each other's company. Put two in a cage and they will often be found hanging out together, so yes, if you can do two females I think that's a fine idea. Alternatively, just get two babies and raise them and if they're both male they won't usally bother each other if they're kept together from the time they're very small.