Lots of good advice here, but don't let it become a big deal - flying in France is pretty relaxed and straightforward most of the time.
Particularly if you're stretching fuel, do try and call to confirm the airfield does actually have it - don't rely on the books. A 12.00 - 14.00 lunch for airfield and fuellers is common.
Frankly a lot of French ATC is very casual compared with the UK, but they are usually helpful, partly because there is so little GA traffic compared with the UK. On trying to get a CTA transit clearance don't be surprised to be ignored for a while - and then dismissed with a "leave my frequency" as soon as you're clear of the area! Unlike the UK, the Flight Information Services eg Paris Info seem to have very good radar and will know exactly where you are.
Military zone crossing will keep you concentrating, though these tend to be very much 9-5 Mon-Fri only, with auto-info services out of hours.
I wouldn't worry too much about landing off-airport without a heli-surface permit. I did it for years with no problems before getting one - which is a bit of an epic, btw. Paperwork important though - there are plenty of Douane looking for something to do!
Oh and most importantly, try not to look too astonished when your landing fee is a fiver for landing at somewhere the size of Coventry!