55 gallons is good for a lot of fish! It's a good size. It's not small and it can house a lot of fish for the rest of their lives. It's just a matter of what fish you choose. A Clowns are ok, but from my experience, they just swim in one spot all day and night and do nothing. There nothing special unless you have something they can host. Like a Frog Spawn or an anemone, and that cost extra because of the lighting needed, but worth it.
Every fish I listed will be fine in a 55 gallon tank, and they are cool looking fish! They each add personality to the tank! The Six Line even takes care of some unwanted pest. So they are good to have.
Just do your research and go from there! Good luck!
Damsels are just punk fish! You can do them if that's all you plan on having. A lot of people experience real aggression from them, but they are cheap and are good hardy fish. Easy to keep. Also from what I learned, I heard Chromis are the same way. They will kill each other off as well.
Fish Sticks, the best thing you can do with your dead fish.