Hi,
I think they breed in freshwater, but will eventually require brackish water as they begin to age. I don't know of anyone who has bred them, though. There is one true freshwater goby, but they are not common in the hobby.
You need a lot of real estate for 10 bumblebee gobies. Those diminutive things are bossy and territorial. I would not put ten in anything less than a 40 breeder. Not because they need 40 gallons of water, but because they need the space. I would also fill up the aquarium with lots of stuff to break up their line of site.
David