Complex question, but I'll do the best I can as briefly as I can...
You can show any duck, some just aren't standardized. The current standardized varieties are black & white magpie, blue bibbed, blue fawn, buff, butterscotch, chocolate, gray, khaki, pastel, snowy, spot and white. It is very, very difficult to win or even place in the top 3 in any show other than perhaps one at a regional fair if you're entering a white. Whites and grays are the most common and popular colors, and you'd typically need an Art Lundgren or Charlie Hodum type of duck to win in those varieties. That's not to discourage you, just to set expectations. It takes a very, very typey duck to win those.
If you're at all interested in showing, I can't recommend mixing varieties with a white. You will never get the, for lack of a better term, pollution out of your bloodline.
I have white Calls for sale, but they aren't SQ, which is why I'm selling these particular ones. Art is going to have some in the next 3 weeks or so, but I can't remember if there are any whites in those. I can check with him if you like.
As Buff said, I'd stay away from crested ducks of any breed. Some people love them, and that's okay, but the crest is caused by a genetic defect that can lead to many health problems. Not always, and not in all crested ducks, but it's something I don't want to have to worry about.