I need help sorting my tank out! :(

[Aquattro]

Hmm, where to begin. first, the large green brittle star will likely eat your fish. All of them. Get rid of him first.
Cowries can eat corals, next.
Beadlet anemones, no idea if they're nice or not.
Which crabs are eating the sand sifter? Hermits? Never seen that. maybe the arrow crab, it will eat your bristle worms for sure. A bad thing in my opinion.
Black spiked urchins are fun, the pain of the spikes is awesome. and they knock stuff over. Actually, they probably will knock everything over. I wouldn't get one. Your mileage may vary...

Other than that, looks good. Some will give you heck for a sailfin in a 90, again, up to you.

good luck!