Kitmiss, there could be an issue with having more frequent and looser bowel movements. Part of the function of the large intestine is to reabsorb fluids back into the body. Without that portion of the intestinal
tract the water will tend to 'flow out.' You may want to consider changing your diet to help control it. Check for posts by Morecambe on this board. He discusses the issue and gives some great and helpful hints on dietary change.
I would think there wouldn't be any contraindications to doing aerobics or other forms of exercise after this form of surgery and a proper period of healing, but be sure to check with your doc.