Rookie upgrade here

[asylumdown]

Decide what it is that you want to keep, and get the tank for that. If you have a hard on for the majestic tangs, start planning a 180 gallon or more. If you really like the cool small stuff (pistol shrimp and goby pairs are so freaking awesome) you don't need such a big tank. I actually just turned my 5 gallon QT tank in to a full time pico tank because the teeny tiny reef organisms that are so interesting to watch just vanish in to the 275.

If all you want is to keep clowns and an anemone, you can totally build a well planned/researched 30 gallon around that. Less to heat, less to light. But if you want some other corals and a few other fish as well, a 50 gallon might give you more flexibility. The amount of work necessary to maintain a larger tank scales with the size of the tank without some serious infrastructure adjustments (a 1 gallon water change is a heck of a lot easier than a 20 gallon water change if your'e doing it with pales and buckets), but also the stability of the system increases with size as well.

In any case: rule #1 is decide what you want to keep, or have the ability to keep, and get the right tank for that. Plan the system, don't let the system plan you.