Thanks so much for your help everyone.
We've decided to go for 5 days:
Day 1
Arrive Las Vegas afternoon
Drive from Las Vegas to Zion
Desert Pearl Inn
Day 2
Hike Zion
Stay Desert Pearl Inn
Day 3
Drive to Grand canyon north rim
Hike GC
Stay GC lodge
Day 4
Hike GC
Drive to Bryce canyon
Stay Best Western Plus Bryce canyon
Day 5
Sunrise at Bryce and Hike
Drive from Bryce to Hoover dam, back to Las Vegas
We thought about Kanab and the other parks, but we wanted to do them slower rather than a whirlwind tour, so 3 parks it is!
Questions though,
Is it difficult driving West in the evening? We plan to drive back to Las Vegas in the evening... will there be bad sun glare?
What car do people recommend? Looking at the car rental websites, probably a standard or intermediate? And fuel up every 50/100 kms?
Worth it to buy hiking shoes?
Thanks so much again