Greg, I had 2 snowflakes, one for 2 years, and another for 10 years. They never once bothered another fish. Anything can happen of course with a particular individual, but they and zebras are about your safest bets for common morays. And maybe I was lucky, but I never had another fish bother them either. Keep in mind that my old one got 30" - they do get decent sized. IMO, you *can* keep one in a 55, but if you can move up to a bigger tank someday that would be better. No rush though.
Your choice of fish look fine.
MBuck, that might work, but puffers and triggers do tend to pick on lions' fins. I would try it - I definitely would choose a puffer over a trigger in that situation. If you see some aggression just pull one of them out. The aggression will likely be only nipping as opposed to killing (such as an ill-tempered trigger might do). And re: eel/puffer, I've done it and it worked out fine.