I had a Pick-up Camper in Germany for 9 months; also traveled to Austria and Italy -- BUT, that was 45 years ago.
No problems in newer areas. Large trucks go there; you could too. However, as previously noted those drivers already know where they can go, you'll have a learning curve.
In the historic towns I parked outside and walked in. That will not have changed. Most any US sized vehicle will not fit on those streets.
We were the biggest thing in all the campgrounds we used, but no issues. Self contained operation will require substantial adaptation, but should be possible most places.
Adapters are available for everything: electricity, propane, and water.
As others have suggested, you are at the upper end of big. I would personally consider something Sprinter sized, and if you are comfortable with being able to enjoy 3 years I'd buy something there and sell it there.