I for say use quarantine for sure!! It does not have to be set up all the time just when you get new live stock and the following 6-8 weeks. Your old 20g or even a 10g would work fine.
Ick is not always in your tank!
Here is a good link to read on QT tanks.
http://www.reefkeeping.com/issues/20...ture/index.php
For a cool small fish I like purple file fish, maybe some smaller wrasses but I don't know what ones off the top of my head can go in small tanks.
Dave