DO NOT, I repeat DO NOT add the damsel!
I have a 60 gallon cube, and added 2 yellowtails as I heard they were quiet and a local reefer was giving them away. They started off quiet and then got more and more aggressive, and then in a flash killed my royal gramma which was my favourite fish. Needless to say I rehomed them after that. A coris wrasse will get too big so unless you’re planning on upgrading I wouldn’t get one. Bangais are cool, I’ve one and am currently searching for a female so I’ve a pair. To be honest, as your tank ages, I think that having fish with more personality is better than colour.
I’ve a filefish which is awesome. His swimming pattern and inquisitive nature is nice. I’ve also always thought long nose hawk fish are cool. Kinda of just perch all day looking around. Clown gobies would be another good pick.
I don’t have a six line, as I heard they can be hit and miss with aggression, but I have a pink streak wrasse which looks quite similar (maybe a bit smaller) which is cool. It kind of just hovers around all day with an orange rim to its eyes exploring the rock work.
Invertebrates like a coral banded shrimp or cleaner shrimp are also a great addition.