not to sound like an old salt, but the first thing you need to do is
BE PATIENT. this is probably THE hardest thing to do when you're new to the hobby. there's an old adage in the hobby that says "good things happen slowly, but disasters can happen overnight", and unfortunately, it's often true.
secondly, a friend of mine wrote a pretty good article on cycling a tank, so give this a read:
http://www.seahorse.org/library/articles/cycling.shtmlfinally, i'd get the largest tank you have room for (i think a 55/60 gal is a perfect first tank, but a std. 29 is about as small as i'd go). there are several reasons for this:
1. you'll ALWAYS want to upgrade as you progress.
2. a larger volume of water means more "fudge factor" if something goes south, meaning more water changes more slowly, and gives you more reaction time to recognize, diagnose, and rectify said problem. this is important if you're a novice, as you may not "see" the problem coming as quickly as a more advanced hobbyist.
3. there are lots of deals to be had now, but $30 for a used 20 gal seems a bit pricy to me. again, there's that patience thing...
4. if you ask anyone who has kept a "nano" as well as larger systems, they'll tell you that the nano requires a LOT more attention and cost than a larger setup due to their inherent instability.
based on your stocking list, my thought are these:
most clowns get fairly large (4"-6" or so), so those cute little ones will indeed grow and put a demand on a small tank's water quality.
also, keeping a 'nem is NOT easy, even
E. quadricolor (BTA/RBTA) isn't a walk in the park. they really require stable water parameters (a mature system vs. a cycled system). the same goes for most sea stars...they really do best in mature systems.
this wasn't meant to be negative in any way, but rather some suggestions from a person who has "been there, done that, and bought the T-shirt" several times over and wants to see you succeed and enjoy the hobby.
