What are they examining your bags for purchased items? That’s gestapoish.

1. Yes they will if they suspect you (age group, clothes, newest phone, certain flights like LAX, LGA) as all custom officers all over the world do. As my bags have been searched every time I've entered the US.

2. You should read up on the Gestapo

US customs won't care if they find new electronics, so they're no problem (they are annoying, with the suitcase thing at port-of-entry, but no problem). As for German customs, I don't know, but: do the initial leave out of Germany over the road where there's checks only in theory and leave from an airport not too far over the border. You can probably get a cheaper flight in the process (e.g. Fly from Basel)

The Germans look for electronics, the Americans look in the electronics and what’s on them.

Fly back through Geneva, and take some basic precautions, such as not taking the box. Done/done.

not nessesarily, but you'll have an issue if they do a controll, or it comes up.