Just personally, I would not do co-ownerships. They seldom tend to favor the non-show/sport puppy buyer. If you do not intend to show or do not know enough about showing, do not bother getting a show quality pup. There will be a premium in price and you might have to give the breeder part ownership and/or breeding rights. If you wish to get a show pup and show competitively, I would not go with white dogs. There are better dogs for show.
The breeder will usually evaluate and grade the dogs at 7-8 weeks. For show, we look at movement, structure, temperament etc. Most breeders will pick pups based on the desired traits for whatever sport or show venue they participate in. A lot of times, it is a guessing game. You keep a puppy, wait till 1 year or so, see how it develops, if it has the right qualities, you keep it, finish it and then enter it into your breeding program. More often than out, they will wash out. If they wash out, they will be homed accordingly (pet, sport, whatever).
I do not understand why you want a show quality pup when you do not intend to show. Get one of the other males free and clear. Enjoy it as a companion.