For a 29 gallon, I wouldn't recommend getting 1 GSP unless you are willing to upgrade the tank when a singleton reaches 4-5 inches. If you're planning to get more tanks in the future, then get some goby. GSP are entertaining to watch since they are active and have lots of personality, but..
I say go with two F8 because you get two great personality interacting with each other. You can try adding in some gobies with 1 F8, but I would rather do 2 F8 with no gobies.
I think dwarf puffers are too tiny (I like bigger fishes). if you really want them, then get 3-4 of them with a school of ottos. Or 5-6 without the ottos.