Most Potter's that I've seen do well also, but IME can be a tad more difficult to get eating than, say, a coral beauty (I worked for a great LFS for a time). The literature I have read supports this. That's the only reason for my comments, not to undermine your experiences.
Pallen, I'd say that 30 gallons is a minimum tank size for this fish; however, your post suggests a future upgrade.

Most of the Potter's you see at the LFS IME are 3 inches or less, so I think one would do fine in a 30 breeder for a while... of course, not as an adult though. Go for it, if you plan on an upgrade. The angel should do fine with the other fish and inverts you have.