imi

Just some thoughts.

Southern Europe, (France, Spain, Portugal, Italy, Greece) may very well get very hot in july and august. These are the months with most tourists everywhere too. I’ll happily ride in 30-35 C, but I find over 37 C to be brutal. June and september are my favourite months down there.
October can be cold and wet unless you’re further south (Spain, Portugal).

The mediterranean coast is over exploited, has heavy traffic, and campsites are very expensive.

Many (most) campsites close towards the end of September.

Typical wind patterns favour riding West to East.

The football (soccer) European Cup will be played in Germany, June 15 - July 15. Riding and camping in a host country during the European cup or World cup can be great fun, as there is a very positive atmosphere over the whole country (hooliganism on match days is typically only close to the stadium, and nothing to worry about otherwise).
Do wear your home team shirt off-bike (even if it’s USA) 😊

Personally, I like riding by the sea or a river, and in southern europe, so my favourite EV routes would be in France: the EV 1 Atlantic coast (north to south) and EV 6 Loire valley (west to east), as well as the Via Rhona.

Following an EV route has the advantage of having more bike paths, thus less traffic, but they can also avoid scenic roads going through pretty villages for example, which can be more charming.
I have reverted to paper maps to find scenic routes. I find Google maps et al often lead me on to stony donkey paths… or the shortest route with more traffic, but miss the less trafficked winding roads through villages.

Following canals can be beautiful riding too, but can get a bit ”samey” after a couple of days. There is often a parallel road connecting towns and villages. The ”old” main road replaced by an A road or motorway is often great riding too.

I prefer poring over a paper map rather than zooming in and out for planning.