first salt tank and scat help

[Ellie_A]

I'm new to this site, so I wanted to introduce myself and ask a few questions too. I'm from Olds, Alberta and I have been keeping freshwater aquariums for about 3 years now. I have a wide range of fish from guppies and mollies to angels, tetras, clown loaches and gouramis to african cichlids. I currently have 13 tanks ranging from 4 gallons to 90 gallons.

One of my tanks (brackish) is currently housing 3 small green scats. I know that they will need salt water when they grow up, so I'm looking into what I will need to do as I have never had a saltwater tank before.
I'm thinking of a 77 gallon tank. I want more fish than just the 3 scats in it though. I'm not sure how aggressive scats get and there's not much info
on suitable tankmates for saltwater. A lot of places talk about brackish tankmates and say they need saltwater when mature, but give no more details, not really helpful to me. Anyone know of any good websites?

I really like clown fish and was wondering if one or two would be ok with the scats. I want to have live sand and live rock in my tank, as well as some corals, although I don't have a clue what kind. I also like the look of shrimp, crabs and starfish. I want to do a lot of research before buying anything, but I don't know where to start. Any suggestions would be really appreciated.

Thanks
Ellie