I'm personally down on Black Mollies or at least the one(s) I have...or should say had. The male constantly pestered the females, charging them, ramming them, pecking at them - no mercy. He chased them all around my 60g tank. The younger of the two females passed away a week or so ago. The older, larger female, passed away just a couple of days ago.
I attribute their passing to his relentless abusive mating behavior. I wish I didn't have him. He's the last of his species now and I don't know if others will come. Perhaps his personality is somewhat unique.
I think you have as many fish as your 10g will support. I think a decent rule of thumb is 1" of fish (when full grown) to two gallons of water - which puts you at about the limit. Others will argue over the math. A lot has to do with how religious you are regarding water quality and providing sufficient swim room in an environment that the fish enjoy (I realize that sounds odd, but I tend to believe that a fish does best in a natural environment or as natural as we can make it in our tiny glass cages.)