I am not new to this hobby but I never had an eel before I will give you a rundown on the tank. its a 46 bowfront I have 22 lbs of live rock in there for him well its my frag tank but I have no fish with him so its a spices only tank about 40 lbs of LBS the tank has been running about 4 years...
mike adding a another large angel would be a very bad idea. but you can add a drawf angel I don't care which two large angels you add they will fight to the death thats almost certain. ;)
for most nudibranches well really do not know what they eat so alot of them die in captive care. but with lettuce nudi they eat hair algea I kept them for about a year or so I found once you run out of hair algea they die off. there one of the easy ones to keep b/c we have an idea of what the eat.