Adding a pool to your back yard never pays. If all the houses in your neighborhood average 1,500 square feet, but you've added a den and expanded to 2,000 square feet, beware. You don't want to be the biggest house in the neighborhood, because you will never get the value. Pick a trustworthy contractor. Make sure the person is responsive and able to deal with challenges.
Price is important, but so is chemistry.
You will be spending months with this person, who will probably see you without makeup or overhear marital spats. Remodeling always takes longer than the estimate.