delta usually just counts it as one of your checked pieces

also , if you haven't been there Albania is awesome as well as greece - typically good weather and a great time to be there

If they are looking for good weather, Norway is certainly a crapshoot

At the north end there might be more snow than you might think- It's been colder than normal lately and wetter so, for example Logan pass in Glacier has the most snow for this date since 2011.

well I have that same situation and i'm thinking of Montanas Vacias

no, its not bikepacking, but it can be super fun and I have definitely found it to be at times much easier than finding a place to camp in parts of europe

I haven't used a bladder/hose set-up for years so take this with a grain of salt, but some people kind the effort required to raise the water from their BB to their mouth by sucking, annoying. I highly recommend a full frame bag but maybe for drinking switch to a stem bag?

over 12c is easy though, under, not so much

You very well might have been close to hypothermia, years ago, touring in SW Montana i had a ride during a rain storm at somewhere around 45f, riding into the wind. It didn't really take too long before i was cold then rapidly proceeded until i was having some difficulty using my fingers- i contemplated stopping and even setting up my tent but wasn't sure i could actually perform the needed tasks. I ended up deciding to continue a few miles to a small town where are cafe was my salvation. I was actually quite well equipped given the season, just not enough for a wind driven rain. Now I go even better equipped since you just don't know

we only ended up doing Bodo to Kirkenes due to some massive travel snafus so i can't speak to south- we just did our best to avoid highways and take roads that looked like they would be scenic (gut feel)

the tunnels can be easy and they can be nerve racking/unpleasant- I recommend earplugs as they are loud. Wow chose to take a bus trough the one up by Nordkapp- best idea of the trip

Gifflar are in every convenience store- highly recommended.

carbon seat stays? I would try to keep the weight down in the rear bags, especially the upper bag- those racks act like a level arm so you just need to make sure the stays can deal with the forces (in a direction they aren't designed for). You very well might be fine but a break would have you walking

i would ask over on r/bicycletouring since it's more of a road tour

The original idea and goal of the seat pack/soft bag set-ups was to have a lighter, simpler system for carrying the needed amount of gear over rough dirt roads, trails and hike a bike terrain. The overall weight was lighter due to the lower weight of the bags, smaller volume and attendant attention to u/L packing. Not having rigid attachments and racks led to fewer failures.

The top heaviness was typically dealt with by putting bulkier, less dense items in seat pack and bar bag and heavy, dense items and water down low. Over time more and more bags have evolved and things like seatpacks have grown. Too, there has been a development of lighter trimmer racks and pannier systems which tend to be the next step up in capacity. For your wants i might start with a full frame pack (you may find yourself using it all the time) and then a good light weight rack and mini panniers. for shorter u/L trips a bar bag and seat pack are great but they do tend to be harder to load and are definitely limited in volume.

It's totally fine to go alone, in fact some times the trip might be better. You'll see more, meet more people, think more etc.

It's just different but very much still good

key is wearing your puffy and leggings (and a good hood or hat) as well as a good pad attachment system- Like like and use katabatics

The inner RDO posts are pretty good as far as comfort, as well as some ritcheys, I like carbon for seatposts

Not sure about the moving parts in the ergon

I do ride a ton in the winter, in the dark -just don't tour much then so a battery light works great

I believe some countries (germany?) require a dynamo light. For me I just have a backup bar mount light or sometimes just a headlamp. It's summer so I don't need a light to see from about 5 am to 10 pm. Mostly dirt road and trail riding here so it's not a huge need

according to NOAA this coming winter is supposed to be a La Nina so chances are somewhat good of a bigger snowpack/ late spring than this year. Starting in the south might increase your chances of being out of the impact area of the SW monsoon before it really gets going with the accompanying peanut butter mud.

trailers are best avoided unless really needed. more to go wrong, more unladen weight

more to deal with portaging etc

20kg is a ton of stuff, often my bike loaded is 20ish KG

Take less and make everything count, then the riding is much more enjoyable

can you just ditch the light? Or do you live where one is required during the day?

if you toss and turn a lot- try a quilt - worked great for me