My wife and I would like to visit YNP for some light hiking and sightseeing.

Our tentative ideas are:

1.) Fly into SLC via STL on or around September 12, spend 1 night in SLC
2.) Rent a car in SLC and and explore YNP for about 4 days.
3.) Drive back to SLC, fly to STL

Questions:

With the above plans, can someone suggest us a practical itinerary with routes for first-timers? Also, I am unclear whether lodging should be done in the park itself or in a town outside the park? Availability?