No, it's best not to chew gum as that promotes digestion. One of the goals of the Master-Cleanse is to give the digestive system a rest.
The salt water flush will flush your system (ie. make you poop!) The first few days of the MC, it will be solid and then it will become mostly liquid. It's called butt pee here in the forum. It is an important part of the MC. You want to get all those toxins out of your body.
As far as smells, it's probably not as bad as you think. The first few days may be a little hard as your body adjusts, but then you get into a groove and the desire for food lessens considerably.