As others say, campsites are good. I'd go for the municipal ones, which most towns have. They tend to be a bit out of the centre so it is worth buying food for the evening before going to the site (more important in hillier areas!). Normally clean, with good showers, and very friendly. Cost is very reasonable, maybe €4-10. I've never been turned away but good advice to get there at a reasonable time.
Some people like the Loire. Personally it's not my favourite bit of France. It's pretty but I found it got a bit same-y, after a few days, riding along mostly flat roads beside a river. I'd rather do the bit you are getting the train for, with the Loire as a destination, but you might like it.
I've used pages torn from a road atlas in France. But, the Loire a velo maps are pretty good for that area.
West to East is more likely to have a tail wind. If you want to get to Paris afterwards it makes sense to do it that way.
Good luck!