Rolled dough gets sticky and hard to handle. Keeping it chilled makes it easier to work with. Work with half or a third of the dough at a time and don't be afraid to rechill it. I sometimes stick mine in the freezer for a quick chill as I'm working with another piece of the dough. A cloth sock or stocking over your rolling pin and a canvas cloth on the countertop make very easy work of rolling out anything.
Bakers prefer unsalted butter for several reasons.
First, salt is a preservative, and good cooks like to know they are getting the freshest possible ingredient. If the unsalted butter they buy isn't fresh, they'll know immediately. Salt can mask off flavors in salted butter. Second, buying unsalted helps them control the amount of salt that ends up in a recipe. Bakers like control, because baking is a science.