Are you going to the Faro bike rally?
I ask because, going the most direct route, it’s just over 4000km return. Take a few days at the rally and you might need to ride a few motorways unfortunately, unless you’re a iron butt rider
My thoughts, for what they’re worth:
Allow time to go through Brittany on both legs - not only is it lovely but there are few main roads, except the coast which will be busy in summer.
Over St Nazaire bridge, Pornic is nice as is Ile de Noirmoutier.
Just south of Nantes is this campsite
https://www.vendee-tourism.co.uk/cam...apdl085v500l0y
A very quiet farm campsite, the owners are bikers and you will receive a warm welcome.
The whole of France is a fantastic place to ride but the least fantastic area is the lower west side - this is where we generally make up time and stick to the main roads.
The Basque coastline is stunning, even from the main roads. Orio has a campsite, a little commercialised but the town is lovely and has some nice restaurants. North west Spain has some of the best food on offer in the world - not just my opinion - especially if you like seafood.
If you’ve never been, then the Picos de Europa is worth at least 1 days riding. From there we usually head west through the mountains dropping down to the coast for lunch, an afternoon swim and to find a campsite. There are lovely fishing villages/towns all the way along - Cudillero stands out for me and there are some superb restaurants in Luarca.
From here I would head south for the Rue da Gasparona on the Portuguese border and follow it, then generally head south through the countryside till you hit the Douro river then follow it as close as you can to Porto - as someone has already said ‘stunning’.
A route from here down to Faro may well be dictated to by time.
On my route home I would cross into Spain and head up to Caceres - I would get there in time to have a good walk round the city - it is quite something.
There is a green corridor between the high flat plains of Madrid and Valladolid that leads to Soria where there is some lovely woodland campsites and a glass of Rioja of course (should you want one).
Obviously there’s numerous passes over the Pyrenees - there’s a good, bike friendly campsite in Jaca.
Any route back up through France, from here is nice:
Carcassonne - a medieval walled city.
Millau bridge
2 motorcycle only campsites - great fun and very friendly
https://www.camping-rendezvous-moto....l-uk.php?lg=en
https://www.motocamp.com/.
That’s just a few thoughts from me - whatever you decide, have a great trip