I had one about 8 years ago. a 5 sounds pretty small to me because he was in a 55G and was all over the tank.
Unfortunately, I didn't do a lot of research when I got them because I was new to the hobby. what I can say, is stock wisely if it's going into anything other than a species tank. Ultimately I think mine starved to death after about 5-6 months, because it was in a very active community tank. Like most gobies, they're not highly effective eaters, and will hide to avoid a flurry of activity. personally, if I were to do them again I would go with at least 20G, and very CALM tank mates. Other than that, I would say bloodworms, live tubifex worms (if available), shirmp sinking pellets, etc, should be staples of their diet.