I wouldn't do gobies unless your going to have a group of Tropheus by itself. The Trets are mean...a solo might work out, but they are incredibly aggressive when breeding....you would end up with a pair of Trets and a zillion fry. It might be better with a pair of one of the Neolamps (except tret)and a pair of the julies(get Regani Kipili) rather than singles of the Neos...if you want some interesting behavior. Having multiple Neolamprologus might work out in a 4 foot tank or might not depending on territories. If you are worried about too much fry with the pairs...get a pair or 3 male Altos (comps/calvus).
Now having all these rock dwellers will leave your upper half of the tank empty looking. This is where the Cyprochromis come in. You will need a small group and they are a great addition. They will fill your water column with color and motion.
Something else to consider would be Cyathothopharynx Foai, Furcifer, or other feather fins....They are real stunners and you could keep a breeding group and they could end up as a nice center piece.
Back to the Gobies..super interesting little guys, but you could only keep a pair cause these guys get very territorial. You will see them in some Tropheus set ups because they leave each other alone and have the same dietary requirements. This leads to the Tropheus idea. Yes, they are somewhat expensive for a group and have a lot of drama attached to their name, but they are an amazing colony fish. The only thing is they are highly addictive and you might wake up at night in cold sweat jonesing to set up another Tropheus tank. This is called the Tropheus Effect. Seriously, watch out for it.
Although I have a plethora of LFS's where I live...I buy most of my Tangs from online importers/breeders/retailers so I know what I am getting. Also, I have had just as much success getting fish air cargo than from some of the stores. Some LFS's that specialize in Africans want way too much for the fish and they can have questionable or shady origins. This is just my opinion and hang-up so don't pay it any mind...I just love going to the airport to pick up fish lol.
