Once switching over to an Atkin's diet, about how long before my body would exhaust it's store of carbs/glycogen and start burning fat for fuel? I would hate to see my weight/waist climb while I'm eating high-fat foods, but before my body decides it wants to burn fat.

Fat doesn't make you fat, just remember that Grams of fat have more calories then grams of carbs or protein so if you are worried you can count calories along with carbs.

For me it takes about 2-3 days to get into ketosis.