Hi Mack,
I will try to answer some of your questions, and tell you what I would keep in mind. But first I have to say I think it is fantastic that you are so active at 77 and bold enough to consider the Napoleon route.
It is quite steep, especially the first third or so. Bring water, snacks, and do not even try to venture up there if the weather is iffy. Stop by the Pilgrim Office and ask about the weather report.
You will see others on the trail, and my guess is that they will be the ones stopping to say hi, ask how you are doing and encourage you. Take full advantage of that company: it is motivating, makes the hike feel shorter, and in April, safer or what will most likely be a quite muddy path.
In April you really should have no difficulty at all with accomdoations, I would not worry about it. But .... if you are using a travel agency, this really should not be a concern. May I ask why you ask about this?
If as you get closer to your departure date, and can work this out with the agency you will be working with, and feel unsure, please do consider the Valcarlos route, which will remain open even if the Napoleon route gets closed due to weather, and is a kinder first day. Also, if you carry a phone, you can always call a taxi on that route should ypu meed one. Orisson will not give you that flexibility if the Napoleon route gets closed as it will also be unaccessible.
Best of luck.