Starting a brackish aquarium...need LOTS of advice?

OK so I haven't bought anything yet but here's the fantasy tank i want to create....it might be too much. Here's what I absolutely need though: I really want a fresh water moray eel, i don't care what kind and the smaller the better. I know they can't stay in freshwater but can they live long term in a brackish tank? Btw, is a brackish tank alot of upkeep compared to a freshwater tank? As for fish, i'd like some bright colorful ones, don't really care what kinds. I suppose i just want some peaceful ones that are big enough to avoid the eel and not bother it. I want a 75 gallon tank, but im willing to go bigger if people think it's too much bioload. As for tank set up I want a big rock centerpiece. I'm going for a tropical rainforest river look. I don't really feel like getting any live plants. I want to keep the tank water low enough so that the center rock will be an island for..(drum roll please) fiddler crabs!!! I figure the eel will eat them so ill have to make sure they're big enough. I'd also like some fans in the tank to create a current. Bubblers would be nice too....will that freak out th eel? I wanted a ray too, but i think that's impossible. Anyways, does this sound feasible or am i dreaming too big?