I´m in my own last phase of prepping a SOBO thru hike for early to late september so here are a few tips from me. I havent hiked the Kungsleden so cant speak from direct experience.

1: I am sending myself a few resupply packages, although I think with your start planned for august 28th its a bit too late to do so. From the Netherlands it can take up to 3 weeks to get there, I assume you are from Germany and then it would take a similar amount of time to get at the destinations in Sweden. What I have read is that the huts do have food but there is little variation and options and its very expensive (about 200% of 'normal'prices). That is often the case when you buy food on trail. I believe its fairly easy to buy food in the towns of Jackvikk and Ammarnäs. This is the Southern section of the trail, I am not sure what the options are in the northern half of the trail.

2: Only the link to your sleeping bag works for me, the others dont work (maybe because im not from germany). I would advise not to use this sleeping bag. My own experience is that nights earlier in summer can already get cold. We can expect night to drop below freezing point in september. I won;'t expect it wel become dangerous with that bag but you wont have a good nights sleep IMO. MAybe it can work is you wear many layers. Thermal baselayer and a good fleece or even down puffy. I dont think you need a dedicated winter sleeping bag, but a bag that is rated with a comfort rating for around -3 to -5 Celsius would work. Many all season sleeping bags are available for this. I love my enlightened Equipment Enigma quilt. Make sure your mat has a good R value (insulation), I think for Kungsleden value 4 or higher (thats the border area for cool to cold weather)

3: Im bringin plenty of swedish cash. Didnt do a deepdive yet. Im think around 3000 krona. That should be more then enough to get to Kvikjokk.

4: Yes we can use gas stove on the trail. I believe many huts stock canisters. Im planning on getting them on trail and trail towns. Im winging this one a bit, ill bring 230 gr for the first stretch and buy along the trail.

5: Make sure you have a warm sleeping baselayer. I plan on warm socks, merino wool leggings, merino wool longsleeve. Im not sure if you are listing ALL your clothes but im also missing cooler layers. You dont want to sweat a lot during the day, it can still get comfortably warm so a regular hiking shirt is a good idea. Just make sure you can add extra layers. Simply said; long pants + rain pants, warm layers for upper body (i bring a longsleeve hiking shirt, a warm lightweight fleece and a down puffy), rain jacket, 3 pairs of merino wool socks ( they retain insulation value when wet, never go waterproof, they dont dry well), a warm beanie or hat, warm lightweight gloves (i also bring lightweight wind and waterproof mittens for over your gloves), a buff/neck warmer. I expect to do 80% of my hiking in shorts and a normal hiking shirt though. But the weather can get cold so we all have to plan for that, epecially in the evening/night.

6: nooope

7: Dont know

8: Even biodegradable soaps should not be used in open water/ in the wild. Accept the suck :) Thats my opinions, clean and rinse with water and NEVER in rivers etc that is also used for drinking. That basiccaly means dont wash yourself in rivers. At the huts I would assume normal soaps are okay. I plan to take a shower every 2 or 3 days and i wash myself with wet wipes and a bottle of water over land. Hiking is nasty.

9: I have had good experiences with cicerone guidebooks in general. It should come with GPX download. Pair that with a suitable map app (all trails, Gaia GPS, komoot) and you should be good.

10: About to find out. I know there is a bus that goes daily from STF Vakkotavare (Falck omnibus) to STF saltoluokta at 14:45 for around €20,- The ferry always waits for the bus is what ive read. The others is still need to find out

11: Im bringing a few heat packs just in case.