As it is your first time touring in France I suggest you make things as easy as possible for yourselves for at least the first couple of days and use autoroutes or other 4 lane roads wherever possible, even if the autoroutes are toll. this will accustom you to 'the other side' and be far less stressful. Also, go to www.viamichelin.com
and get a route - you can choose options on type of roads and also for car + caravan, and you will get a route which shows you the exact signs you will encounter.
As in UK motorway / autoroute fuel is more expensive than supermarkets. At a supermarket - often in a 'Centre Commercial' you will usually find pay at the pump section marked 24/24 which avoids having to weave through various obstructions to pay at the kiosk. Most of these pumps now accept UK chip and pin cards, and will offer you a choice of language as soon as you insert your card. always take the 'recepit' option, and it will be printed after you have fueled and returned the pump nozzle to the pump.
If you have time look back through this forum and you will find lots of good advice for 'first timers' - and we were all 'first timers' once. It's a holiday not a contest and worth spending a little extra to make it a good one. Second time you will wonder what all the fuss is about !
Have a great time.