1)
As @Shelley159 writes, changes in trip length only affects future bookings, and you should of course respect your current 2 listings, not try to change them (but I don’t think you were planning to, either 😀).
Also agree that shorter stays might be a better choice when you are fairly new hosts. I have been hosting since 2019, and still only do shorter stays. My min is 2 nights, max is 7 days, and the typical booking is 2-4 nights, sometimes 7. I don’t want them here longer! 😉 Mainly tourists who come to Stockholm for a mini-break, or stop here as part of a tour. Amazing guests!
2)
When guests stay 5 nights +, I offer clean sheets, and they change sheets themselves. (There are always extra towels.) If I did longer stays, I would definitely want to be able to do a light cleaning now and then, to also be able to check on the place.