I am an incurable scrap addict. I say the more the merrier. And I rarely pre-wash my fabrics, and frequently mix prewashed with unwashed. I've never had any serious problems. Yet. But if it's really going to be a scrappy, I wouldn't worry about mixing batiks with traditionals with reproductions, whatever, whatever. Just go for it and have fun. That's the idea of a scrap quilt.
That being said, I don't know if I would do this for a first project. You might want to try something a little more simple and controlled where you know what to expect. Scrappies are fun to me because I never quite know what I'm going to wind up with. But that can be a little disconcerting for a beginner who's not all that confident yet if you don't like what you wind up with.