We have a 10 team mixed but play with salaries, so no one is filled with just stars. It works for us. If you don't play with salaries, then I think 10-12 mixed would be ideal.
Baseball is a game where a curve is an optical illusion, a screwball can be a pitch or a person, stealing is legal and you can spit anywhere you like except in the umpire's eye or on the ball. ~Jim Murray