The main roads are paved, but there are sections of the road in varying states of disrepair, so in the summer, when you'll be traveling, you'll run into numerous construction delays where the road narrows to one lane, and traffic backs up waiting for the pilot cars to lead them through construction zones that go on for miles. The last bit in the Yukon, leading to the Alaska border, is especially notorious due to "frost heaves," undulating pavement where the roadbed settles due to melting permafrost. If you hit those dips at speed you can go airborne! Where there's construction, there's gravel, so you need to be a little bit careful of the truck traffic. (You'll see LOTS of trucks, lots of RV's, and a surprising number of motorcycles!) The business about screening your windshield and carrying extra spare tires was good advice back in the day, but that hasn't been necessary for quite some time. Do make sure that you've got a good full-sized spare tire (less than 8 years old) and a functioning jack; you shouldn't have any issues. I got one "star" on my windshield on my two-month trip, and it happened on my last day, on a paved highway in Arizona when I was almost home.
I totally understand about the possibility of medical issues. I've had multiple back surgeries. All I have to do is move the wrong way, or sneeze when I'm not braced for it, and I can throw my back out to the point where I can't even walk, much less drive, and I had nightmares about something like that happening in the middle of nowhere. I was extra careful, and I was just fine.
Like you, one of my main interests is photography, and the trip yielded thousands of wonderful images. I don't do Instagram, but I have a little personal website with photo galleries that play like automated slide shows.
Here's the
Phoenix to Fairbanks segment; and here's
Fairbanks back to Phoenix (by a different route). There are many other smaller photo galleries from that trip (and many other trips), as well as some articles in my blog about my planning for the drive. Glancing though these pictures just now, I'm half tempted to join you myself! (Unfortunately, I'm way too busy these days!)
Enjoy, and be safe,
Rick