what coral safe frags and snails are best???

Banded Trochus Snails - can flip themselves back over and the best looking IMO won't grow to big either.
Scarlet Reef Hermit Crabs - least aggressive and less likely to attack snails for their shells, also the best looking of the basic crabs IMO.
These are the only 2 that I use in my 350 SPS only reef.
For some reason I don't find these in LFS very often, maybe because there more expensive I don't know. I have always gotten them from Liveaquaria

 

Blue leg crabs, emeralds, certh snails, nassarius snails should all do fine, some may say red legs but the ones I've had in the past liked my zoas!

 

i had bad luck with a emerald crab. he ate all my zoas and GSP, and liked to take chunks out of my nassarius snails when they got to close. my blue legged hermits frequently kill my astreas and nassarius snails, but seem to leave the margaritas alone. I bought some ceriths, and I'm not sure if its them, but every morning I have spots that may be eggs on my glass that i have to scrub off. That being said, my current mix is astreas, nassarius, and margaritas. I still have 2 hermit crabs i think, but I'm not replacing them as they die. Oh and I got rid of the emerald crab long ago. Be warned, they can be a pain to catch.