Finally got out for our first ride on a beautiful late morning today. It went very well. We started out practicing for about 5 minutes in an empty parking lot - starting stopping, coasting, pedaling, figuring out what we had to communicate about, etc.
Then we went for about a 10 mile ride on combination "bike" path (MUP), streets and sidewalks. Absolutely no problems. The starting, stopping and standing still went without hitch. We found that the coasting comes pretty quickly to the stoker. Stoker had no complaints about speed, and after just a couple of times, quit being anxious about sitting on the seat with feet on pedals when we were stopped. I was pleasantly surprised that our cadence preferences are close enough to be workable without any significant adjustments.
I'm a clipless pedal rider (MTB and road) and my wife has never used them. It seems pretty clear to me, and I think she's also seeing the logic, that clipless pedals might be the way to go for her. There were a couple of times when I shifted that her feet were bounced off the pedals and then it was a little trouble getting them back on. I think I'll get her a basic pair of walkable biking shoes and the double sided (platform/spd) pedals to start with. For myself, I'll probably just go with an extra pair of SPD pedals I have in the box of spare parts.
Aside from lubing the drive train, adjusting the crank sync (they were about 1/3 between parallel and 90 degrees) and trying to adjust the shifting, I made a couple of changes before the first ride: replaced huge original tires (1.95") with some Ritchey Tom Slicks in 1.4. I also bought a pair of Forte Fast City ST/K 1.25" based on a recommendation in this thread. After I'm sure that stoker is comfortable, I'll try them and then decide on which I like best. Rejects will go on my MTB commuter conversion.
I also replaced the front tractor saddle with an old MTB saddle I had, and replaced the high rise front bars with flat bars and bar ends for my comfort. Left the tractor saddle in the rear, and adjusted the stoker cockpit to mimic her hybrid bike.
We went over some pretty significant bumps and pavement cracks and she said it was fine. We will have to tweak her cockpit a little, but no big deal.
Aside from needing to work on the shifting and brakes some more (new bike cable stretch it looks like to me), we had a great ride and both enjoyed it. I definitely feel this will work out for one of my major goals: for us to go on a ride together at an exertion level that will allow me to get a workout without freaking her out.
Thanks again for your advice. So far so good!