It's perfectly ok to keep just females. The issue with Guinea fowl is they behave like turkeys and prefer to roost at the highest point possible, rather than going into a hen house. Therefore unless you keep their wings clipped they will be up in the trees as soon as they can fly. Personally I like to see them being able to express natural behaviour like this but appreciate it's not practical for everyone.
Also like turkeys they are susceptible to blackhead, so ensure all your poultry is wormed with Flubenvet regularly.