new tank help

hi all,need some advice.

i just set up a new marine tank last saturday.
23 gallon
1.5 inches of crushed coral and a bag of live sand
2 powerheads,1 circulating the other to drive a seastorm 100
1 hagen 50 ouside filter

my local aquarium shop says i could put some green chromis in this saturday,,
but i have also read that live rock will help get through the nitrification cycle.

what should i do?
also,,i have the seastorm 100,,should i use a air drivin protine skimmer ,,dealer wants to sell me a powerhead driven,,says air ones no good?

thanks ,,hans