A good rule of thumb, as far as how many fish, isn't how many fish but how many inches of fish will go in your tank. I've read in multiple sources that 1 inch of fish per 2 gallons in your tank. So you could conceiveably have 45" of fish....BUT you have to take into account the bio load that fish AND inverts put into your tank. Add your fish slowly; meaning 1 or 2 fish every couple months, check your water parameters and add 1 or 2 creatures until you get to your 45". The others are SO right about the mandarin fishes please don't add them until your tank is at the very least a year old. You have enough live sand and live rock now but your tank doesn't have enough of their food for them to survive yet. Research all your fish carefully and see if they will get along in your tank too. It's such a helpless feeling to watch one of your fish being beaten to death by a tank mate and you can't catch it to save it!