I do a tour of Europe most years, always VFR. I normally do 18 hours in 7 days. That is very relaxed and allows you to cover a lot of ground. I would look at the long-term forecast, decide which direction, fly in to an airfield with a Transair or similar and pick up the charts etc and go. In summer, south of central France you are very likely to get good weather. If you want to take it a bit more seriously you could probably do 25 hours in 9 days but I would take some time to enjoy the trip. When asking for advice beware the “club expert” who has never been more than 1 hour from home base.
Rod1