Wow, thanks for all the nice replies, everyone! I'll try to answer your questions:
Routing: the road network is really quite straightforward through these remote areas. I could easily have memorized all of it using Google Maps and Street View. However, I did prepare a GPX track using plotaroute.com and uploaded it to OsmAnd on my phone. I used that a few times around Steinkjer and Levanger in order to find my way. I used my Forerunner 935 as the cyclometer. It is very energy efficient, and just needed some topping up during the ferry and the sleep stop. I also used my Edge 820 to check time in hand for the ferry crossing, but I didn't bother charging it after that. It is simply too power hungry for long rides. So yes, I did bring a power bank for charging watch, phone, as well as the camera.
https://www.plotaroute.com/route/836461
https://www.plotaroute.com/route/842674
https://www.plotaroute.com/route/842718
Light: It really is bright during the summers over here:
https://www.timeanddate.com/sun/norway/trondheim
I had 21 hours of daylight per day, and from 23:45 until 2:45 there was what's called "civil twilight", which is still reasonably bright. I didn't really need the headlamp for this ride. Further north in Norway, at 66,5 degrees north, you would cross the arctic circle, and the sun stays up 24 hours. A few years ago, we visited Svalbard and the world's northernmost settlements at 78 degrees north. It was odd to leave Oslo in dusk and see how it got brighter as we flew north into the night. When we got there at 3:00 AM, the sun wasn't only visible, but it was as high on the sky as you would expect mid-day.
Gloves and glasses: Yes, I suppose I should keep them on. At some points I just didn't bother finding them. I do have clear lenses, and that's going to be useful during night riding in France. Da Brim does look useful!
Gravel: There wasn't a whole lot of gravel. The section at 12:24 in the video was a 5 km long shortcut (included in the brevet route, I hasten to add). The long section starting at 17:27 went on for 18 km. Yes, this was also the hilliest part of the ride. I am very happy about the MTB cassette setup I wrote about here:
https://forum.cruzbike.com/threads/solo-touring-in-norway-on-a-loaded-vendetta.12618/ I use the lower gears all the time. I also use the top gears, of course. Sometimes I wish for a 53T chainwheel, but I don't want to sacrifice my low gears. I don't find the Vendetta to be very harsh on gravel roads. As long as the road is smooth, I have no issues. Of course, a road filled with bumps and potholes is less pleasant than it would be on a DF. In short, I would much rather do 23 km on gravel with the Vendetta than 577 km on asphalt with a DF
No close calls, but there's still a limit to how fast I dare to go downhill. I'm getting faster, but so far I won't go above 60 km/h (37 mph) on this bike. If there's a gust of sidewind at that speed, it's a little scary. I'm sure that's just how it feels, and that both the bike and me would have been able to handle more if I had to. I've also read on this forum that the handling has been improved since the Vendetta V1.0, and I would be very interested in hearing from somebody with direct experience with this. But all in all, I'm very happy with my bike.
If any of you ever want a guided tour over here, let me know! You can ride my Vendetta while I take the Bacchetta
Ed, I'm looking forward to see another Cruzbike (or more) in the recumbent start group in Paris!