Sorry, no time to read every reaction (so maybe doublure):
a perfect area to ride and to meet all your wishes is the Loire and Cher valley.
Castles (Chenonceaux and Chambord, the finest, resp the biggest) and more historic sites, scenery (sunflower-fields, swamps, vineyards), moderate temperature (Provence, my other favourite is too hot in summer), cuisine etc.
Safe routes and trails.
But no mountains, an extra challenge or desired scenery for many people.
Loire Valley was the playground for many kings etc. in the past. And they appeared to have a good taste for locations to enjoy themselves and their maitresses (and the other way round)
Bonne route!