We were in Zion, Bryce and Yellowstone mid July last year. it was HOT. like 97 on July 4 at Zion. We made National Park reservations a year out, but local campgrounds more like 4 - 6 months. its seems you are not camping though. Hiking in the mornings and evenings was fine, not difficult to get on Zion Shuttle before 9 am. Took local advice and didn't try Bryce in the early AM because of traffic, and had no issues with driving all the way through, various lookouts and short hikes, and then the Queens/Navajo loop before sunset. There is no grocery store anywhere near Bryce Canyon. and not very good restaurant options. Springdale UT has everything you would need.
Highly recommend Zion Adventure Company! We hired a guide for the Narrows hike, comes with water boots and a hiking stick, and then added e-bikes because of changing Covid rules about shuttles. The wonderful Miles met us in town, got us outfitted, we rode through the park instead of waiting and cramming on the shuttle, and hiked the Narrows. definitely a bucket list experience, made so easy by the Zion Adventure Co.
Consider checking out Dark Ranger Telescope Tours in Bryce. small groups stargazing with great "guides" - in one of the last light pollution free areas of the US.