Fish choice

[BMW Rider]

I'm ready to add some more fish to my 130 gal reef. I am considering a few possibilities and would like some feedback on them.

Current fish stock is:

Yellow Tang
Foxface
Tomato Clown
Pink Spot Goby

Obviously I have room yet for a few more smaller fish, one that I would really like is a Royal Gramma. I'd also like to have some that will be good in a small school. I am wondering about some Green Chromis, or other Chromis. I am a bit hesitant as I don't want anything as bullish as a damsel. Are the Chromis more peacful than their Damsel cousins. Another possibility I've though of are some Cardinals, preferably Banngais. A third choice would be a couple of firefish, but I'm not sure about them with the Pink Spot goby all ready claiming domain at the tank bottom. I also have heard good reports on the Six Line wrasses too. Any other suggestions are welcomed.

I also need to get some sand cleaners in there, and Nassarius snails seem to be a popular choice. How many of them would be appropriate for a 4" tank. Would a conch or two be allright as well or should I just have one or the other.