all your flame/powder gouramis are still dwarf gouramis, they are just breed for those colors. You might have to ask your LFS to special order female gouramis for you, I know that's how my friend had to get his here. 125 is A LOT of room for gouramis, but they will still chase each other around with no end if one ends up being a bully.
When selecting pearls, i doubt you'll be able to sex them unless they have been established and are a bit older. Pearls don't show their sex traits until they are a bit matured and feel established in a tank.
Those 3 may work out, i'd keep an eye on them...in that 10g they might get feisty. I would STRONGLY advice taking your time and just go with those 3 powders for now. If they work out in your tank, (and i know that may be in a month or more), well if it works out then add more! BUT you could just see first hand how those 3 take to the tank, and go from there. And please post here on the boards and let us all know, Gouramis are my fav!