Dave -
I agree with your sentiments - and, yes, doctors can really talk down to you, at times.
Which hardly helps somebody to make changes and get better.
I've come back from a Stage IV condition, I'm pretty darn chunky, and I'm 20+ years older than you.
But, I've also ridden all my adult life and rode through my illness, too.
Here's what I did - starting small -
1. I rode a few humdred miles in a loop. 2014
2. Then I rode halfway across the country. 2015
3. Then I rode all the way across the USA. 2016
Remember, that 3# was, like, my 8th X-USA ride.
I don't know how much riding you have done over the years.
Also, riding a bike with gear is a totally different animal.
But you can do it - if you start with a reasonable goal.
I have found that if you pile too much on, too quickly, it all comes crashing down.
Nebraska might be a good place to start - - close to Colorado.
It's way more scenic than Kansas, light traffic, all the little towns have camping.
The towns are closer together in eastern Nebraska - western Nebraska has some big distances.
Also, there is weather - sometimes pretty serious weather.
If you haven't ridden a bike in a long time - I would suggest the Katy Trail.
It starts just outside St. Louis and crosses Missouri.
it is pretty level all the way and has no car traffic.
Plus, there are lots of camping lodging options along the trail.
https://bikekatytrail.com/West to east might work better since there are fewer users in the western half.
Would your wife be willing to take you to trailhead in Clinton, Missouri?
Can you change a flat? Do you mind getting rained on? Being hot & sweaty?
I think you could do it, easily, in two weekends and the week between.
Of course, it sure wouldn't hurt to do some prep riding beforehand.
Plus, acclimate yourself to riding with panniers on the bike.
You don't have to be a pro to tour, many people learn along the way.
But, again, start moderately and then work up.
Best of luck - Jama