There is not enough space in a 10 gallon to keep a coral banded shrimp and an emerald crab together long term. A standard coral band shrimp gets quite large, and they can be very aggressive when defending territory from another invert. There is no room for an urchin or starfish in that tank now.... without the coralband you could have managed a short spine urchin (purple urchin) but there is no species of starfish available for that size of a tank.
With the coralband shrimp you'll have to be very careful about what fish you add, as if the shrimp feels at all crowded he can also do a lot of damage to a small fish.
Please remember that a 10 gallon saltwater tank is not the easiest thing to keep going to begin with. The smaller the tank the harder it is going to be to keep stable and healthy. Water params will fluctuate very rapidly, salinity will do the same thing. 1 inch of evaporation in a 30 gallon tank is not equal to 1 inch of evaporation in a 10 gallon. Likewise, an ammonia level of 1.0 in 30 gallons is going to affect the fish differently than an ammonia level of 1.0 in a 10 gallon. Everything in the smaller tank is going to become toxic quicker, and your oxygen levels will deplete faster, too.
Your best bet at this point would be to return the shrimp and replace it with a short spine urchin. The emerald crab should do ok provided it's a female. If it turns out to be male it is possible it will have issues with your fish later on, so you'll want to watch that closely.
How long has this tank been set up? How much live rock is in it? What kind of filter are you running? What are your water params at for ammonia, nitrite, nitrate, pH, and calcium? Have you checked calcium yet?
Best of luck to you, I hope this helps.