Have you tried KTM/Husqvarna, I bought mine from the dealer. I have a 901 but the dash is the same shape and size as the 23 onwards 890's. Locomoto is another option.
I take it math's was not your strongest subject at school. ;):p Sorry couldn't help myself.
I bought a new air filter for my 1979 TT500 last year (45 years old) I had bought one about five years before when I started the project but that one started falling apart from age, they come oiled, and...
I have a set on my bike, they do make a small difference with the vibration and add quite a bit of flex to the handlebars.
It's very important to get the gaps right when installing them.
On the open road with luggage your fuel consumption will be worse than around town. Wind plays a big factor with fuel consumption and after 100kmh it becomes exponentially worse.
Have not checked your ride report yet but I'm looking forward to reading though it since I've done some of the same...
I always check everything the bike shop touches when I get my bike back. Trust no one.
Suspension settings are a personal thing and easy to adjust so I wouldn't expect a bike shop to do them unless it was a shop that specialized in suspension.
It does help that I have a technical background...