First time to Grand Canyon (or anytime) --- South Rim, Trailer Village. Hike rim or down some. Take a mule ride down a ways. Enjoy sunrises and sunsets all along the Rim.
Zion for short stay unless you are very serious hikers. We love Bryce and glad you are going to Cap Reef as it is once of our favorite place -- nice hikes in both places for all levels of hiking. Love Arches and do the Island in the Sky section of Canyonlands - south section is a long drive from a stay in Moab and only for kinda serious hiking and not much else there.
See www.LaurenBarbara.com and the Wanderings link for pictures (not sure why they did not come up as a link on here as I went to the section that should post it).
Also email me at LaurenH517@gmail.com or send me a private message if you would like; I would be glad to help you.
Enjoy - we love all these places and have been there several times.