Done a few bike-packing trips in Europe and also silk road mountain race which is at the more extreme end of things. I would say you are massively trying to overplan it. Flexibility is definitely a positive thing.
So firstly I’d get rid of fixed on and off days. My personal preference is generally no days completely off the bike as I find the day after a complete rest day feels a lot worse than having a relatively easy day, but YMMV. (The exception is if I’m passing through somewhere particularly interesting where I want a full day seeing the place). Generally easy days work themselves out without any planning, at this time of year bad weather will likely dictate some times you’d rather not be on the bike!
Also off days can be practically difficult if you are wild camping, or quite boring if you are at campsite in the middle of nowhere. So if you do decide to have an off day try and do it a bigger town where you actually have stuff to see/do.
Similarly, get rid of fixed distances or times. No problem having an average goal in mind. But let everything else dictate the exact distance each day i.e. camping spots, resupply points, how you feel etc.
Regarding pacing, the suggestion of not looking at power and just going for a really easy RPE is a good one. I don’t know how Friel accounts for altitude, but ime there is quite a big variation in how people respond, so it’s something you really need to “wait and see”. With all this it’s much better to go too easy than bury yourself in a hole.
In regards to nutrition, the Alps are just not that remote. You will never be too far from a cafe/restaurant/supermarket/petrol station. Nearly all of which will sell energy drinks. The sugar and salt option will work, but it’s a fair bit of faffing and then you are stuck carrying the rest around, and no doubt sugar will end up getting everywhere in your bags. Personally I take electrolyte tablets to put in my water and just drink a coca cola or Fanta at stops.
Again, I wouldn’t overthink it and worry about getting exactly 60g of carbs per hour.
Total kcal over the day is a much more important thing - you probably can’t eat too much. Remember it’s touring not racing, nutrition doesn’t have to be optimised for perfect performance, you are not bonking at 0.5IF because you had no carbs for 1 or 2 hours.
You plan to ride less than 6 hours per day. Good breakfast before you set off, boulangerie stop at 2 hours, and then a decent sit down lunch stop around 4 hours should get you through alone. Of course feel free to use energy drink and snack on the bike for some extra kcal.
I would suggest carrying a few emergency gels just in case.
Compression socks don’t weigh anything and pack down pretty small. If you really want them and have space I don’t see why you wouldn’t bring them if you think they are beneficial. Although im sure the kinds of people that cut the handle off their toothbrush to save weight would disagree!
