My suggestion on walking and stretching is try using the Couch to 5 K plan. You don't really have to plan to do a 5 K but you can learn so much by following their plan.
Here is the link
Couch to 5k - C25K Running Program and this site is also really good, gives you the schedule and some ideas for walking/running and stretching
Cool Running | The Couch-to-5K ® Running Plan
Remember you don't have to run to get the benefits, it is important to keep moving.
I saw that someone goes to a Zumba class, that is FUN!!! I went to one once and it was great.