Ur bang on with ur list of fish. The Coral Beauty might be in trouble too though unless u have plenty of hiding places. The Picasso is a beauty fish but for sure would nip the Lion's fins, and everything I've read about them they can be model roommates until one morning when they wake up, go postal and kill off all their neighbours, so for as cool as they are I have begrudgingly left triggers off my wish list,I have a coral beauty, a mated pair of clowns, and a solo maroon. The clowns "co-exist" but I think adding another pair would be a game of roulette until I fired up my 500 gallon system but that won't be until about May, I have a multi color angel, Lemmon peel, and a heraldi angle. A sailfin tang, yellow tang, hippo tang, melanarius wrass, and 3 different types of Gobies. Hawk fish have an appetite for my cleaner shrimp. How attached are you to ur Nasso if you want to do a little horse trading? The Eel would be fine with the residents you have. I keep him well fed and he is very well behaved. Almost too docile. I almost have to slap him in the face with a silverside before he will take it.
IMO there are a couple options for u. Unload a ton of livestock to make room for Lion, keep everything u have and just add the eel and hold out for a dwarf Lion.
Cheers bud