I love having more than one!! They are SOOO much fun to watch as they play.
It really depends on the person when to get a new baby. Some would rather have two to potty train and get it over with at one time or some would rather wait until one is older and can help train the baby. I would rather mix a female with a male, just make sure they are fixed
Don't mix two stud dogs together...that can be BIG trouble later on.