good info ax, nice to share it.
schoolkid, let me know if you need a recommendation of a reasonably priced , but perfectly fine hotel in Nantes. We stayed there on our first day of riding and explored the city for a day before continuing on. Neat city and I highly recommend seeing the mechanical elephant and the site of the mechanical stuff, easy to see with a search.
you didnt mention, but campgrounds are common and a great option to use, but you havent said if you are campers or how you plan to do this trip accomodation wise.
its a fun route. We crossed France following the 6 to Basel, Switzerland, and overall for the vast majority, its a really nice route with mostly paths and very quiet small roads, so nice to be able to chat.