x2
A brackish tank would be killer. You could have large plants over the top of the tank/mangroves in the tank and stock it with various archer fish. Watching them shoot down prey from the leaves would be awesome. I've kept mudskippers and they are fun but I always wanted to a large archerfish tank. I got 15 mangrove trees you could have. All over 12" tall.
Archerfish
Dragon gobys
BW flounders