It is very addicting. I started with a 10 gallon tank. That was not big enough so I upgraded it to a 20 gallon. I am now in the process of setting up a 38 gallon. I am sure once I get that tank filled and stocked I will upgrade or start another tank.
I think that the lighting is one of the key issues you need to address. If you are going to want corals, the lighting will be one of the biggest purchaces you need to make. Then you need to decide on MH of T5's.
Bryan