I would just stay with what you have and see how you like it. Down the road you can upgrade to something bigger and just move over the rock to the new tank. For such a small tank I don't expect there to be a long cycle but I would definitely wait till your parameters are stable.
yeah, thats what i was thinking^, the only reason i would upgrade is if i saw a REALLY good deal.
i might slowly buy the new supplies like sand and the tank