1. First and foremost you purchased the home to live in. What type of set-up would make you the most comfortable.
2. If you are truly only going to be there for 5 years or less, I would consider not doing the Master addition. Even if you add a basement bedroom with an egress window and tons of natural light, it is still a basement bedroom.
3. You are correct a 2 bedroom is tough to sell. This is considered a starter home in Broomfield. If a family with younger children purchase the home they would want everyone on the same floor, not in a basement bedroom.
Hope this helps