Keep in mind that a tank is only cycled for the amount of fish that are in it. That means that when you add more fish, you will get a mini cycle until the bacteria colony catches up. It can last from a day or 2 to a week or 2 depending on how much you increse the stocking level. Since you have 6 fish now, if you added 6 more fish, you would have increased the stock by 100% so you could expect a fairly decent mini cycle. Later on, when you have say 30 fish, adding 6 would only be increasing the stock by 20% so the mini cycle would be small to non-existent. I would suggest going slowly, only adding 3 or 4 at a time until you get a larger stock.
The fish you have aren't what I would call extremely active fish (not like danios) so it is odd that they are swimming that fast. Their behavior shouldn't be much different than in the tanks at the LFS unless those tanks were extremely crowded to the point they couldn't swim. Usually swimming quickly (more like quick darts) from one end to the other and hiding are signs of stress. If your ammonia and nitrite aren't both at 0 then that could be the problem. Other than that, I can't imagine why they would be behaving that way.