If I could offer some advice on continental touring in a spamcan as follows:
Don't do more distance than a tank full of gas a day, i.e. 400 miles tops, any more becomes hard work instead of a holiday and the best laid plans of mice and men get in the way of rigid schedules, things such as weather and hangovers knacker up early morning starts.
4 people plus bags in a 172 is pushing things, best do it with no more than 2 so you're reasonably light and not arguing over schedules and trying to please everyone.
You'll find that the French and Spanish ATC are fine and used to dealing with duffers, although the Spanish seem a bit more rigid on paperwork and flight plans, a hold over from Franco's days I'd suppose.
Download a few apps for economy hotels like Ibus so you can book them before getting into the circuit and if they are all full move on down the line to the next town/airstrip and try again.
Plan on getting your ass reamed on avgas except in Jersey where they are giving it away for a song.
Take a socket set and some screwdrivers for the odd fix that will inevitably pop up.
And most importantly enjoy yourself, flying over there is a great experience and good learning curve.
Think that's about it!