I would suggest going with a 55 gallon, minimum. The dwarf species are very shy and tend to be strictly nocturnal. In other words, you'll very rarely see them. So I would suggest looking at the more mid-sized species. They are more outgoing in general, and will warm up to you, interact and display all the behaviors that make octopuses so fascinating to us.
If you look through some of the the other octopus threads on this board you'll find most of the information you need. If you still don't find the answers to your questions you might go to TONMO.com (The Octopus News Magazine Online) and check out the boards there. It is a site dedicated to cephalopods of all sorts, but there are forums specifically for octopus care and the various kinds that are commonly kept.