For feeding, Lionfish like to eat things that are alive and kicking so you need to break them of this habit. The way i did mine was give him some ghost shrimp live and he will suck up 10 in a quick hurry then let him go for 2 days next give him the ghost shrimp in a pair of feeding tongs live and make him eat them off the tongs (he will trust me)
wait 2 days then feed him dead ghost shrimp off the tongs.
these things have a huge appitite so when you feed him a small meal and let him go for 2 days he is ravenous and will do your bidding once you open the lid. beware he may go after your fingers in between feedings.
anyways, once he has eaten from the tongs once or twice now you can get him to take silversides out of the tongs. You will probably have to wiggle the silversides to make it look like its moving. If he's hungry enough he wont care, he'll eat anything at that point. Now i throw him ghost shrimp for a snack and feed2 silversides every other day. my lion is 9-10"
feeder goldfish have no nutritional value to the lion at all. fun to watch but all it does it make poop that you will have to deal with if you don't have a superior cleaner crew.
The lions are very beautifull but they really limit what you can put in the tank with them because they eat anything smaller than they are.
no shrimp of any kind unless its lunch, anything with a large shell around it should be ok. turbo snails, hermit crabs ect. large eels are good, good sized urchins, large starfish, and most fish that are larger than he is and will not nip at his dangly stuff
Good luck
The key to getting them to do what you want is to make them really hungry, once they do it once or twice they will see that that is how they get thier food
