as long as you keep an eye on your nutrients, you'll be fine adding a few chromis. From what I hear though, you'll want to do the green over the blue reef, as the blue reef are more aggressive (think damsels). I've only ever had the green ones, and have never had a problem with them.
I've got a 38 too, and my nitrates are never over 5 with:
2 small tomato clowns hosting in an RBTA,
1 green chromis,
1 Potter's Angel
1 Solarensis Wrasse
1 Kupang Damsel
1 Yellow Watchman Goby
1 Mandarin
1 Clam,
and lots of corals - mostly softies, zoos, shrooms, and LPS.
I do however, have a sump with a very good skimmer & a HOB fuge.
I agree with the idea of adding the RBTA before adding any prize corals - mine did move a little bit, and luckily didn't harm anything before finding it's permanent home. Before you get one though, make sure you cover your powerhead and filter intakes.