What is the optimal depth for the substrate to be at? I'm hearing 1to 2 inches, and anything more than that is asking for trouble. Is this true? I'm thinking of a 1.5 inch sand bed at the moment.
It depends on what fish/inverts you're planning on keeping. You can have a 1/2" deep sand bed and be perfectly fine. I don't subscribe to the notion of their being an "optimal depth", otherwise everyone would do it and no one would run bare bottom systems.