Oh wow. This is crazy. I just came back to check on the forums. I don't think I've posted here in years. Anyway, the photo you posted is of my old goby. He/she died a couple of years ago, I think from the dreaded red tumors that afflict this species. It was in brackish water though.
To answer your questions, they are estuarine fish, so we tend to think they more or less require brackish water long-term. I've heard of them growing to 60 cm (2 feet) in only a year, but their growth rate seems to vary a lot, possibly based on feeding and water quality. My friend (a former LFS owner) told me that someone had brought one in once that had grown up like that very quickly and was then eating its tankmates, so keep in mind that they may do that when they become larger. Oddly enough, that rapidly growing individual had been kept in freshwater, as have all the other very large ones I've heard of. I wonder sometimes if they mature in freshwater, and then move to brackish areas to live (and to the ocean to spawn). People say they're blind, but I don't really believe that. They're very territorial, and before it died, my violet goby would follow me and strike its aggressive pose at me, as well as attack my hand or the net. Because of this, keeping more than one of them together is probably ill-advised, especially if they differ in size by enough for one to effectively bully the other(s).
I'm more into fish that don't get that big now, but it was a cool fish to have. I'd still love to see a fully grown one in person.
