Thought I’d note a few things learnt along my roadtrip to Provence here, hope it helps anyone planning to visit France via road. 
Card acceptance
Outside of the big cities, there’s still a 10% chance merchants impose a €10 minimum card payment. If you like visiting markets or use laundry service, always have cash although most sellers accept cards.
Petrol stations & motorway services
Beware of the €150-170 temporary hold each transaction. If you refill AdBlue and Diesel that’s €150×2 pre-authorised. I used credit card for all refuels without any problems, but if you have limited funds on your debit card this might be an issue.
As for fuel price, Total Energies are the best IMO. While their diesel was consistently at €2.09/l, I saw Esso charging €2.60, Shell was €2.40 and supermarkets were around €2.22. (UPDATE: As of 31st March, Total has sold out their fuel which they bought in on the old price and new price is updated from April. This is still a more ethical practice than their profiteering competitors.)
Using French motorways is a much more pleasant experience than in the UK. There are regular services (Aire) to rest at least every 30 mins, many has a canteen and shopping essentials. There’s no equivalent of Gloucester services, but most Aires are about 50% of that experience.
For a smoother experience passing toll roads, we used a Toll Tag from Vintrica which got us through the barriers within 2 seconds, saved loads of hassles getting in and out to pay the toll. There are other companies like Bip&Go, Emovis etc., but we chose Vintrica as they have more countries covered than other services hence the higher price.
There’s no point in avoiding toll roads like in the UK as you’d waste far more time on the roads.
Service opening hours
Boulangeries and museums open up until 18:30 even on Sundays surprisingly, but bistros and bouchons in Southern France don’t serve food until 19:00. I’ve been told anywhere South of Marseille, dinner service isn’t available until 19:30.
Each towns seem to have different preferred days off rather than strictly Mondays/Wednesday.
Northern France takes their Sunday closures more seriously, with all supermarkets close at 12:30 on Sundays.
Miscellaneous
Beware of parking restrictions if you drive anything higher than 2.1m as there are more height barriers in retail parks and local free car parks. This might be due to far too many motorhomes taking the mic by using free parking lots overnight and hardly spending any money on local services. It might also be local camp sites and hotels lobbying their council to protect their trade.
Speaking of campsites, many are still closed for the winter season and refurbs until April, more so in the South than the North.
PS: @AlanDoe Could French petrol holding charge and Monzo in France [Discussion] be merged into this thread since it’s linked to 
app’s Welcome to France -More travel tips?