I did not take the signposted walking route. Instead, I cycled on the main road which often runs parallel to the walking route. Those main roads still had Camino signs and warning to drivers to be aware of Camino walkers and cyclists on the road. It is very safe to ride. Drivers are used to cyclists as there are plenty of non Camino cyclists on the road as well.
From Santiago, it is again easy to cycle to the airport. Once you reach the perimeters of the airport, there is a separate walking / cycling route which takes you directly to the terminal building.
Later while relaxing in front of the cathedral, I met many other cyclists who are on more expensive and sophisticated mountain bikes. I talked to a couple of them. They have taken the CF route. According to them, taking the walking route even on a mountain bike was difficult and in some parts, they have to walk with the bike. They agreed that it would have been easier to do it in a hybrid or even a road bike on the parallel road rather than taking the walking route.
There are few places in Santiago which offer cleaning, packing and transporting the bike to various parts of the world. When I asked them one of those companies quoted £100 to take it to the UK. Of course, most airlines will take about 35 to 50.
The North route is hilly. On some days it involves climbing 3000- 4000 feet. Minimum was about 1500 feet. Therefore this will usually be classified as challenging or level 3C. But of course, you can do it at a slower pace.
If you have any questions, please do ask.
Buen Camino...