My advice is listen to Ray
We visit France routinely and have been further afield to Spain, Belgium, Italy, Switzerland, Germany etc. many times. Best tip I would give is to have some way of accessing the internet while out there (we have Three mobile sims) you can plan as you go along and see if you're right next to a place of interest that you may have overlooked. Consider stopping for decent meals, sleep and showers (we use Ibis cheap and cheerful hotels) so you all feel human and refreshed. The 8 is fairly epic for these types of journeys TBH.
Enjoy, and take pictures. We all like pics!
John