Thanks to all for the input.
A bit more information:
I don't know yet when I'll be able to make the journey, but I don't want to leave later than the 1st of March, that's why I can't cross the pass of Great Saint Bernard on foot.
I love camping, I'm the kind of guy who would rather sleep in a tent than a five stars hotel, so I'll try to include as many campings as possible, if they are enough to justify the excess weight of a tent I'll bring it with me (I have this:
https://www.caminodesantiago.me/community/threads/santiago-to-rome.51831/#post-570264). Otherwise for emergency only a tarp or a poncho will do. I don't do "wild camping" in a non wild areas, so my concern would be to find camping sites open in Spring.
The reason I want to get to SJPDP is because by the time I'll get there I'll probably be on the road for a couple months already, so I may want more company than the previous route had offered me, or I may be fine and in that case I'll opt for walking the Norte.
I want to visit Lourdes, but I may change my mind during the journey. But during the planning I want to include it as my destination after Santiago would be Fatima. So, I would regret to pass so close to it and not be able to visit it.
The Le Puy route would be much more straightforward to me if coming from Geneva, otherwise if I take the Montgenevre - Arles route, I'll need to walk up from Arles to Le Puy and down again to Lourdes and up again to SJPDP. All this can be avoided by taking the bus to cross the tunnel of Great Saint Bernard, stay on the Francigena to Lauseanne, then walking to Geneva.
I'm still unsure, but probably a 30 min bus ride will avoid me a lot of ups and downs and crossing Turin...