The tank I'm guessing would be between 2,500-5,000 gallons. I know that's a big range, but I'm hoping for more to 5,000. Substrate shoudln't be too hard to get. The only thing is that I might want to get some monster rays. Gotta make sure the substrate would be okay for them. For temp, where I am, it can get cold in the winter, and almost 90 degrees in the summer. For the cover, I never really even thought of that. I'm not really sure about that, but it definatly needs to be escape and jump-proof, as I plan on getting arowanas. For water changes, I could probably get a big rubbermaid drum, maybe two. And for rocks, I don't know where I could find big pieces, but I could easily get could medium or small ones.