If you run your figures and they check out, then you should of course be OK. I'm just not sure I'd want to fly in that area in an a/c with a service ceiling of 15k ft and the associated sluggish performance once you get close to that. But as you say you know the thing well.....
On a different note re your insurance: in the US in general the renter's insurance is '50% earned' on inception. That means that if you cancel after your trip, you get 50% back, not any pro-rated figure.
For ground transportation just call the FBOs, they can and will arrange that. Typically the lineman will drive the rental car right up to your airplane
You could also drive from Flagstaff to the south rim of the Grand Canyon. Takes about an hour and a half. Hang out there a little with your child, then back to Flagstaff and go flying. If you do decide to overnight at GCN, make sure you check hotel availability! The place does get crowded...
PS: if you like beer, there's a great microbrewery in Flagstaff, right across the tracks from the train station!