Sounds like a great trip. You should be there before the summer crowds, but may have to plan for some possible chilly weather. Have not been to Arches or Canyonlands (there are on the list), but just love Zion. Hike the Narrows if you get the chance (depends on weather and water levels and you need shoes and clothes that can get wet). I would also try and add Bryce Canyon to your list. We did a short visit there when moving cross country and it is spectacular. If you go, hike down into the canyon and through the canyon (we did it ourselves; no need for a guide). Get up and watch the sunrise over the canyon and it will be a lasting memory. We still talk about it 23 years later. Utah is beauitiful and almost otherworldly. Enjoy!