My dad has had a colostomy bag for over 20 years, You sometimes see it when he it gets full of gas - he can't fart so the air you would normally expell from farting goes into the bag blowing it up like a balloon. The only time that you smell dad is when he has emptied the bag (never go in after him) and if he is leaking, (which doesn't happen often). He changes his every 3-4 days dependant on the plaster situation.
It is easy to get an infection, particulary if you have a plaster attachment, as it rips the hairs out on the belly, which may be come infected - this has happened a couple of times. - if its a new stoma this is also prone to infection without proper care, after all it is your intestine on the outside of your body!