I was able to upgrade my little pacman from his tiny carrier that he was kept in at the store to a 10gal Long right away. Granted he spent his first week hiding out underneath the eco earth substrate until he got more comfortable with poking his head out. For awhile I could only see his eyes if they were even peeking out of the substrate.

If brian really wanted to, he could divide the 20gal Long into two separated 10gal sections and house two, or some other critter if properly divided. Or leave the one half empty until the Pacman gets bigger; and then it could have a lofty 20gal to itself.

I think the key things to keeping a Pacman is keeping the temperature around 70-85 (Night/Day) and the humidity at 75%+.

I've read a few threads where Pacman owners have trouble setting up the humidity and maintaining it throughout the day, which causes some health problems when a Pacman doesn't have the right amount of moisture in their environment, personally I have a see through glass top for my 10gal that holds in most of the humidity in my bedroom. It's also thin enough that I can adjust a daylight/heat lamp to occasionally increase the temperature of the terrarium as needed.

Some people say that they don't need the additional light/heat but I think that is up to the owner and careful consideration of the actual enviroment that the Pacman terrarium is housed in. My family runs the A/C 24/7 in my house during the summer, so I leave my heat lamp on the terrarium throughout the day to keep it nice and warm. Wouldn't want our frogs to freeze to death now do we?

As for humidity being important, there were a few forum members that had issues with extremely low humidity levels, causing their frogs to practically hibernate and "play dead" or estivate would be the proper term. Pacmans don't move around much to begin with, but you don't want them to be uncomfortable.