I have had a household of 4 dogs for the last 15 years or so, for me, the house seemed awfully quiet when I'd lose one to old age, so off I'd go, in search of a 4th.
The "cons" of having 4, are, the expense, the clean up, but that's about it in my book.
The "pros" are so rewarding, they are a hoot to watch with their antics, I have a blast training them/working them in different venues, they are all
differing personalities and each has it's own niche in my life.
Don't get me wrong, there are days I think, gosh if I only had two!
As for the gender thing, I have two females, two males, aussies & GSD"s, one of each gender. I have always had male dogs, multiple male dogs with absolutely no problems, the girlz do have their spats occassionally, but it's no major thing.
Again, as far as gender, I'd rather have two males, vs two females who can be real "bitches". I say go for a temperament that will compliment the dog you have now, if you have a pushy male, make sure you don't get another pushy one, etc. A good breeder will match a puppy to your existing lifestyle.
I also tend to wait atleast 2 years in between dogs, I like to have the ones I have, in a place, obedience wise, before I introduce a "green" dog into the pack.
Diane