there are very few marine fish that will school. some will shoal, but gobies are not one of them. Gobies have no swim bladder, so when they are in open water, they dont float, hence why they have a fused pectoral fin that is used like a suction cup too help them cling to rocks, sand, glass, ect...
while neon gobies dont school, nor shoal for that matter, they may hang out together. IMO it would depend on the tank size, and if they form pairs (ex, if you get 3 and a pair forms, then the third will be chased from the territory). I would personally get maybe 5-6 and let them form pairs. a 180g should be big enough for several territories.