I have some Spanish and French VFR trips on my website. They are quite detailed and were written to assist people doing long trips.
San Seb no longer has Customs so cannot be flown to/from the UK directly (a 24 carat stupid decision but so many airports are not run for aviation purposes).
Those RAs off the west coast of France tend to be inactive at weekends, but a smarter procedure for VFR is to always plan two routes: one which is assured, and one which you actually want to fly. Then make the selection once airborne and when you can get French ATC to advise on the activity of e.g. R31A1 or whatever.
Obviously watch the French nuclear power station areas. Notams and current charts are a must for foreign flying. In the UK you can be sloppy but if you do that abroad you will one day get caught with your trousers down. The French especially have bizzarely arrogant ways of dealing with this stuff.
Sadly I am also one of those who does occassionally say that posters need to ask well formed questions if they want people to type up long detailed answers. This issue appears on every internet forum and is not getting any better as the years go by, mainly IMHO due to the proliferation of smartphones which have brought out a lot of "low effort content creation", but their owners are still somehow expecting others to spent time on typing up good replies. It just ain't going to happen, and that is why when you do a but of google research on almost any topic you dig out hundreds of web forum discussion hits pointing to long threads packed with banal one-liner posts and you have to spend hours wading through all this... and most of them are dead ends. Whether you like it or not, human nature is what it is, and this is why the quality of online discussion is declining - everywhere, not just the aviation forums.