I have not spent much time in Germany, but I believe it is not technically allowed except for specifically marked (signage) sidewalks. It's just accepted basically everywhere. A Goldwing is very nearly as big as a Smart FourTwo, I would suspect that if someone complained you would get a ticket. Best case, a bemused policeman laughing and asking how you managed to get it up over the curb.

Germans are surprisingly relaxed about rules, despite the reputation. If nobody will get hurt, then it's usually not a big deal in my experience. This is the country of the autobahn and Oktoberfest. Compare that to Switzerland (where I have spent more time); there the police will give you stern warnings even if you haven't broken the law. They are very "just-so".

Usually yes, if it's not in the way of pedestrians. The MC/scooter parking laws (and filtering for that matter) are surprisingly lax in Germany. I've only once seen a MC to get a parking ticket and this was even warranted as it was blocking a entrance to a house/garage.