Hi Guest,
I wouldn't worry about getting two bitches, especially if you plan on different breeds and ages :) It seems that the ones who have the most likelihood of developing problems are either the same breed (some get along, others don't :rolleyes: ) or the same age :)
There's lots of advice on this board on how to introduce and first live with two different dogs --- just do a search :)
Good luck on your quest :)
toodles