Chevy, a 12" and a 10" tang. I call that dinner. You have some herd there, even for a 200. I personally would not put moorish Idols in that tank. The only reason I say that is because of the stock you have. You will have to feed the Idols at least three times a day, four would be better. And they eat a lot. I don't know how you would do that with those other large fish in there. I think they would steal most of the food. My Idol is the largest fish I have by far and he is able to push the other fish away, but a 12", 10", 8", 6". 5" etc fish will be hard to out-compete. Idols have no defense mechanisms like tangs and they can't even bite anything (very weak mouths and tiny almost non existant teeth)
In the sea they eat a diet of mostly sponge which very few other animals eat so they have any competition. They also live in very shallow water so most of their companions are smaller than them. I saw many more of them while snorkling in 10" of water than Diving deeper. I don't know if you will even have luck with Idols in a 400 gallon tank with those large fish. Their longivity depends a lot on how much food you can get into them and how often you can feed them. You know about my feeding dish but it only works because none of the other fish I have will eat pellets. For the third feeding I always feed with a baster. I need to get the food to the Idol before the fast eaters steal it.
Anyway Chevy, that is just my opinion, I could be entirely wrong. I can only go by my experience. Now if you diden't have those two large fish, that would be an entirely different story.
One more thing, While my Idol eats almost anything, He will not touch nori.
About feeding bananas, I freeze them then slice off small pieces just like I do for clams. Freezing them makes them a little tougher and they stay together better. A moorish Idol will not eat anything large. They can't bite hardly at all.
Have a great day and good luck Chevy.
Paul