I've only been to Reims and Epernay (getting there by train.) Each of these have tourist offices which can give you maps of the region and hours of the tastings and tours. Many of these close for lunch from 12:00 to 14:00. Since you have a car you can cover more ground than on foot. Even though Piper Heidsick (sp?) is a "big name", they have a nice tour--they use a mini-train to go through their underground caves--worth taking.
In any event, don't miss going to the Cathedral in Reims (the tourist office is a block away.)
PS: During the summer "tourist" season, most of the champagne houses are open 7 days a week.