New to saltwater??

[strezman]

Hey all, so i've got myself a 30gal tank with all accesories incl. filter, powerhead skimmer and half decent lighting. its been set-up for just over 3 weeks now and id like to know a few things?? i've been told by numerous ppl that i should not be introducing fish yet, but several other places say it should be fine. i've got about 15-20 lbs of liverock and a bed of live sand. i've had 5 hermits a feather duster and a few mushrooms in there for a week now and they seem to be doing fine. i had my water tested regularly through out the 3 weeks until my levels were up to par. some say the amonia level will still spike, but why would others say its fine?? can you help me? i would like a fish soon? thanks.