Kay:
I walked this route this September past.
I gather May and September are the big times for the Camino walkers. June is a bit calmer; July and August are more family oriented summer holidays and short term walkers who tend to stay in one place. The owners of Gites in France in fact have different markets.
To organize your accomodation, get the Miam Miam Dodo, a reference guide focused on accomodation. It is generally available (and there is a Camino oriented shop in Le Puy). This highlights a small subset of places; there are lots more advertised along the route and the Tourist Offices may also be helpful. Also, if you do not speak french, you can if fact decipher MMDD.
Get a european phone if you do not have one. I got a cheapo and recharged it as required. You should be ok reserving one day in advance - my experience is based on a September walk, the busy time for geezer market.
Lexicon:
Gite Communale - Similar to a refugio in Spain, often supported by the Commune (local government) and generally quite simple. About 10 Eu, no supper but usually cooking facilities.
Gite de Passage - varied accomodation ranging from dorms to 2 bed rooms suitable for couples, etc. Generally, it is possible to get a Demi Pension, which means bed, supper and breakfast. This will cost about 28 - 35 Eu per night and is a very good exposure to regional cuisine.
Chambre d"hote - Bed and breakfast but also has supper (demi pension). This can be worthwhile since in some of the smaller communities or rural Gites, there may be no other option. Around 35 - 40 EU.
Watch out for Sunday and Monday. Many services are closed on Sunday and Monday for holidays so these are good days for long walks but, you might have carry a bit more food if you are not staying in a place with a demi pension. Buy food on Saturday morning since a lot of places can close on Saturday pm
Language: Ideally, french; if not connect with bilingual folks (from Quebec?) or take advantage of tourism offices or others for reservations. You will be able to get by.
All the best
Frood