desem questions

I'd like to start a desem using the Laurel's Kitchen Bread Book recipe. This will be my first, and already I'm thinking about cheating. (Sorry, I'm just loose with recipes and can't be reformed.)  First, does the dough ball really have to sit in 10 lbs of flour?  Has anyone tried using less?  How does the dough know whether it has 10 lbs around it or 3?  Second, has anyone used a desem starter to make a mostly white loaf? 1/2 white 1/2 wheat maybe?  Any thoughts?  Thanks.