For a first timer I would recommend joining one of the major clubs and using ther services. I happen to be a Caravan Club member so perhaps a bit biassed towards them, but I'm sure the other offers good service too.
Get a copy of CC Caravan Europe volume 1 (France and Spain) which contains a wealth of information plus member's reviews of sites. Don't get too ambitious on your first trip (but unfortunately, like many countries, the "real" France is not the bit along the coastal strip but deeper inland ( and I write as one who first went to France in 1957)
Be aware that twin axle vans are not welcome everywhere in France, particularly at municipal sites. You don't actually say when you are going, but unless july/august you probably don't need to book months in advance for sites.
Assuming you have not driven there before, use the autoroutes until you settle in - many of these are toll, but worth it until you gain some confidence - there is much less traffic on them except immediately round the ports.
Where to go depends on what you want to do. Personally I'm not one for big cities and enjoy most the small towns and villages and the countryside.
The only equipment beyond that you use in UK you will really need is an adapter for the hook up - many French sites still use a round pin plug and may or may not have an earth connection - all this is detailed in the CC book.
You cannot change British gas cylinders in France, so suggest you take two full cylinders with you if going for more than a couple of weeks.
Moneywise take more than one credit/debit card and keep them apart in case of accident with one. Some supermarkets will need proof of identity but the Euro version of the photocard driving licence works most places.
Nationwide Post Office and some others offer cards which are commission-free for hole in the wall withdrawals in France, so don't take wads of euros from high commission exchanges in UK.
I could go on and on; one final tip - take it easy, don't try to do everything at once and above all enjoy it - a wonderful country and generally nice people - just like UK in these respects.
By all means keep using this forum if you have more questions - that's what we are here for.