Hello Michel,
What a wonderful project—after all the extraordinary trips you’ve already taken! Your profile photo is simply stunning and reminds me of Mali... Where I cycled for a month in the Dogon Country. It was my only way to get around, and I loved it.
You don’t specify whether you’d like to go through Italy or France, or where you’d take a boat.
Have you considered the ViaRhôna? I think it passes through Isère if I’m not mistaken, but I imagine other VF members will have all the info you’re looking for...
https://www.viarhona.com/
I’d say spring would be the best time, though that’s just my personal opinion... (it rains then too, of course).
For Italy, I assume you already know the EuroVelo site:
https://fr.eurovelo.com/italyFrom a girl who cycles but never very far (only in my head!).
Too bad I’m not on your route—I would’ve happily welcomed you! (I joined an app called *Guidon et Couettes*—free hosting for cyclists.)