The Master Cleanse is a fast so it definitely affects your metabolism. To offset the effects as much as possible, take it slowly when you transition back to solids. Eat many small snacks instead of meals at first. Listen for your body to tell you when it is hungry (or full). Chew your food until it is practically liquid and eat slowly. Also stay as active as possible to bring your calorie burning back to normal.
As for the veggie soup, do not need to add broth. The veggies you use will be enough. Try not to use too much water. You can always add more if the soup starts to boil down. This will keep the nutrient value high for the water.