they are filter feeders in the water column. several need a specific food size to be happy. the easiest way to do this is to feed blender mush. you will need to keep your skimmer cranked in order to remove the food before it rots.
it is not really the number of critters that are needed it is the ability to process the food put into the tank fast enough before it rots that is the trick. you need a monster skimmer for sure. lots of hungry critters help a lot also, but they need to be the kind of critters that would eat blender mush right away. algae eaters do not count.
since you have a SB and an unknown skimmer we will keep the bioload a bit light. i would suggest a firefish of somekind, a six lined wrasse, and a pygmy angel. they tend to be least likely to pick at corals. if you do not plan on having a whole bunch of corals than a flame angel could be a good candidate.
these fish were picked because they are planktonivores, for the most part. this will allow you to feed blender mush for the crinoid and the other fish will be more than happy to eat the bigger pieces. a good cleanup crew will also be good. a good amount of cerith snails will be needed.
blender mush is what you should be feeding your tank if you have a crinoid. since they tend to only eat food of a certain size blender mush is the best bet. it contains a lot of different sized food particles.
here is a recent thread on blender mush. there is a big one around here somewhere, could not find it right off the bat, but if you do a search for blender mush i am sure you will find many recipes. the object is to blend very lightly. just enough to get rid of the really big chunks, but not enough to make it completely liquid.