need help bigging a tank

Just realized I never actually answeres your question.

You could go with a HOB overflow box. Eshopps are garte. While I have never had one, I know some people use them & the design is nice, as apposed to other brands. There's another brands HOB OF box with the same design as the Eshopps, but I forget the name of it.

Eshopps: Overflow boxes

See the baffle in the little box? That keeps the water at a constant level, keeping it from running dry.

 

...some good starter fish...look here!

Nano Fish

Beginner Fish: Tropical Fish for Beginners in Saltwater Aquariums

Don't go with any fish that aren't considered 'reef-safe'. These fish will nip at corals & maybe an occasional clam mantle.

I have a coral beauty (dwarf) angel, which is 'reef-safe, with caution', meaning it may nip at corals. Though many people have successfully kept this fish in a reef tank.