There is a great variety of frozen food available. V2O offers many types.
11 fish in a 55 gallon tank is an awful lot. I guess the best advice i could give you is to research each fish and see what their needs are. I know my tang won't eat mysid shrimp, but loves algae pellets. My PJ cardinals like New Life Spectrum Pellets and dont really like mysid that much. My Clown will eat just about anything, even tries to eat me if i stick my hand in the tank. Liveaquaria.com is a great tool for researching each fishes individual needs. I don't feed my coral betty often, but reef roids is good, there are a couple others, their names escape me at the moment.
The guideline I've heard is one inch of fish per gallon. I don't know if I would adhere to that, you have to use your own discretion. If they arent getting too aggressive, or fighting, and you can keep your tank parameters in check, you're good. I have a 55 gallon, and i have 4 fish. One off them is a small yellow eye tang, and i wouldn't mind getting one more fish. But that would be about all i would want.
Each tank/system is different as far as the bioload it can handle goes. And different fish differ as far as their needs in a tank. Managing nutrient levels and fish interactions will determine the stocking of the tank.
