Welcome to this mad group!
John, I think you are on the right track, but please consider staying on just two wheels. You may want to start with a big, balloon tire model and work your way up, or down, on a real, modern comfort bike.
I am 71, and have road bikes, comfort and mountain bikes to ride. All are different, all are fun, and it is just a great fitness tool for anyone who is still able to do this sort of thing. Now, if you don't already walk a great deal, then I would start with about a mile or two every day, no excuses. This will begin to build you back up with no strains or pressure. Once you can take a good walk with ease, then you can 'graduate' to a bike. You will find out quickly how important strong legs are.
Where I live, there is seldome any long, level straights, and gears are a must, unless you want to walk your bike up the hills. Good luck. Riding bikes is like a second childhood, and everybody needs a second childhood to make up for putting that all aside to be an adult.