Up to a few years ago I have always kept bitches together without any problem. I had 4 bitches and one dog. He was the boss and used to lie on the rug like king tut while the bitches gathered round and washed his face and cleaned his ears
I still have 3 bitches living together now.
At the end of the day the choice is yours. What about the breeder who you purchased your girl from do they have more than one bitch? Perhaps you could speak to them and see how theirs get along together. Most of my friends have multi bitch households with no problems and if you are going to have them spayed then I thing either sex would be ok.

good luck with whatever you choose to do.