I would suggest, seeing how your 5 month old likes the new pup before making a command decision. With 13 now and probably 14 by the end of the weekend...we're pretty good at intros. Put them both on a leash and let them meet each other gradually...you know...smell, smell, lick, lick!! lol

As far as gender, we have both and all get along well...except for the occasional sibling rivalry. I am a HUGE proponent of spaying and neutering...it's much healthier for the dog and they seem happier too. Much less testosterone floating around and less likely to fight.