As a German I totally agree with this list of beautiful small/mid size cities. I would like to add Ulm to the list as well.
Germans can have very different mentalities depending on the federal state you are in. So maybe try bavaria and but also something in the very north.
Avoid Berlin at all cost since it's not representative for Germany at all.
I know you prefer cities but I have to say that I am from a small village and there you will find the most German Germans in existence.
I have a Google Pixel with my home country SIM in the slot and I only travel with eSIMs. Almost every country offers eSIMs but they are usually more expansive than the same data with a physical SIM. However I am willing to pay a bit more for convenience and if ever I need a physical SIM, I have a second phone so I do not need to remove the one from my Phone.
Have been in many countries in SEA, Vietnam and Thailand included and both of them have good eSIMs, especially Thailand.
German: Digitaler Nomade
Depends completely on your needs. I prefer a small check-in luggage and a backpack in the cabin with all the electronics. I mostly move around with cars and never have a problem carrying a luggage. If you want to move more freely you might wanna choose a backpack.
Wise and Revolute is very different. Wise does not protect your money and hence should always only be used for small amounts. Revolute does:
https://www.revolut.com/en-DE/legal/deposit-insurance-information/