8 days seems like a pittance and here we add favorites to your itinery already.
How could you possibly do it all. Duesseldorf has the most outstanding modern museums, google K20, K21 (art bought (no joke) by the state take of their lottery!). You can see around 50 Paul Klee in one spot, maybe a dozen Chagall all on one wall, ... Beuys .. the Kunstakademie .... the river, the Kommoedchen (cabaret), Opera, Schauspielhaus (excellent) ....
If you want to see and are a visual person (may I assume that as a photographer you are.) here is your chance! Go spend days in the museums.
And Cologne added here for good measure; why not Berlin and Frankfurt, too, just another couple 2 hour stop ... for US tourists on speed skates ...
Then Munich with the Alte and Neue Pinakothek, Galeriestrasse just North of Odeonsplatz, Nuernberg with its churches ...
I reckon, we around here are just fast visit junkies.
Ddorf might be doable in 4-6 nights. Munich in about 8, Nuernberg another 6 (don't forget the NS Party sites!), Bamberg a week, ... The Alps and Innsbruck, maybe 2 weeks to just acclimatize to the the elevation and air ... never mind the gear you will need in winter to get out of doors ...
And all in 8 days, all over. Advice asked for just 3 weeks in advance, how timely that is ...
So: Forget it; that is my advice.
Do not plan or ask; just get in over there and walk about the hotel neighborhood that may be the best plan. * cities in 6 days *
If you or i had but 1:30 hour for the Louvre or the Hermitage or Moscow between planes/trains. That is what I would do: smell the air and come back quickly ...
What a waste of jet fuel this 1-week to the edge of the universe tripping is ..., though.
Sorry to spoil your adventure with a shot of reality and opening your eyes to the vast-, hugeness of your effort.
Unproportional, unreal it seems, and a bit decadent, maybe, some could say.
