You will be fine cycling across France.
If you only done around 30 miles max then that's it, momentum will keep you going.
Camping is fine, plenty of campsites, even better municipal campsites.
a mobile phone is enough to do google maps, contact your mobile provider to ensure free to roam abroad.
Share the load with your with wife, take a stove and pan. Sleeping bags, water etc. Don't over do with food, just enough to keep going during the day, plenty of Lidle, aldi around.
Keep to west France if flat, it relaxing being by the coast.