I just got my first saltwater tank today and I'd recommend guppies or maybe some type of tetra. J/K

Are you going for a fish only, fish only w/live rock, coral display, or something in between?

I think that decision will dictate how many and type of fish you'll want.

It's a good thing you're thinking long term, because you'll be going down a lot of dead end streets if you don't have one.