My wife and I have done many long rides with my wife as pillion on an O3 FZS600
Longest were Cork IRL to Angers Fr via Rosslare Irl to Pembroke UK, Dover UK, to Calais Fr to Angers Fr in 30hours.and
Valkenburg NL to Cork IRL via Calais FR to Dover UK and Pembroke Uk to Rosslare IRL in 24 hours.
We have We have ridden from Nerja Sp to Cherburg Fr over 5 days after spending 3 days in Nerja Sp, 1 in Madrid, 3 in Biarritz Fr and final night in Granville Fr
Nothing is strapped to the bike everything is in the Non Fango Panniers, Top Box and a tank Bag.
Tank Bag holds the most likely items to use for easy access. A tyre pump and puncture repair kit, very small Seely Multi Meter, documents are all under the seat with the tool kit.A very small socket set in the top box and a half litre bottle of engine oil for topping up if necessary. Oil Level guage is very sensitive in the FZS600
Top box also has the lightest items like shoes and some light clothing to change out of the boots to walk around in.
I would suggest changing the rubbers on the passenger footrest to the same ones as the rider footrests, they are more comfortable for the passenger.
Stop for a break for at least 30mins every 250-300Km then fill up with fuel first prior to having a snack and a drink, don't eat to much , can make you sleepy. If you feel you have to stop more often do so, after all it is a holiday.If you don't have an alarm use two disc locks with yellow reminder warning strings to attached to the disc locks and handle bars as they are the easiest to carry.Keep one or two half litre bottles of water in the tank bag for easy access. Dehydration can be an issue.
Pillon would need to be used to rides of over 300km before doing the journey you are doing., if not you are going to have a sore rear ends.
I don't use Sat Navs just maps and don't always use the main thoroughfares as you have to be more aware of where your are going than you do when following a satnav blindly. I do have a satnav on my phone which is used in emergency if I come across diversions that direct me off the route I have taken due to incidents or road works.
When packing for the trip pack light, put what you think you both might need on a bed or table and then put back half of it, people always over pack clothes and return after only using half of them.
It sounds like a great trip, be cautious as to where you park the bike, as the last thing you want is to have it stolen.
Enjoy