I have a tuxedo urchin that is fabulous and likes to decorate himself up with shells and things he finds as if he is getting ready to go to prom. He cleans up the rock well too. However...He also has decimated my zoa garden and knocks over smaller frags/corals that he finds. I'm thinking about rehoming him. I could be unlucky with the one I have. Many people have them without problems.I agree on urchins. I'm personally partial to tuxedo urchins - I think they have a lot of "personality.'
Just about everybody in my tank has a job in one way or another. I have cleaner shrimp, tangs, starfish, gobies, blennies, various snails, red and blue hermits (they will jump a snail for a shell btw). I just add things as I need them. I started with a couple shrimp, some hermits, and some turbo snails. If I think I need more, I research if I'm buying something new, and then add more. Due to the size of your tank, your cuc will eventually need to be quite large. But you don't need to go out and buy everything at once.