i'm guessing wait until good parameters? what kind of crew would u suggest for a 120g that could end up having any type of coral in it eventually? (undecided)
As usual, Len's right...there really isn't any need to spend money or waste the lives of the cirtters until the tank starts to settle out. As far as a clean up crew, that kinda depends. Most people use a combination of snails and the small hermit crabs. Do you have a sandbed?
Hermits can be problematic, but I like to have a few red legs just to watch as I think they are interesting. Rob's list of snails is pretty much what I prefer as well.
I like the above as well but would add conches as well. I had 5 but lost one when I knocked over a piece of LR during a rearrangement of the scaping. The other 4 I have had for 8 months or so and are all growing and eating well. I think they just look cool.