I'm not gonna toss the fish in for a couple of weeks


You're still not quite comprehending the amount of patience required with regards to water quality. A couple of months to stabilise quality is more realistic, assuming that you don't have any major problems along the way. If you do, then you can easily add months to that time. People have been known to have to wait 6 months before adding fish, although that is extreme.

Powder Blue Tang is indeed a beautiful fish, but prefers larger tanks, 100G or so. It's also quite pricey at $50.
I'd recommend a Damsel to start - most are 'low maintenance', more tolerant of smaller tanks, and below $10. I'd also suggest looking at a clown and anemone, many varieties of which also fit the easy/small/cheap model. (Make sure that the anemone/clown pair that you choose are symbiotic...not all are).