Most cultural differences between Americans and Germans are minor and not big deal breakers (though the exclusivity thing might be), but it’s important to keep an open dialogue and build a relationship founded on trust where you feel free to share your thoughts with one another.
So if you ask if that dress looks good on you, they will answer.
In America there are general rules for dating – you meet someone, you ask for their number or Facebook, or ask them out.
If you ask them how they are doing they will assume you ask as you want to know, not to be polite.
Likewise, if you talk to them they will assume you do so because you want to get to know them, not because you are being polite (unless you are left alone with them in an uncomfortable situation, of course).
Dating can be confusing as it is, so when you add dating someone from a different culture it can get downright crazy.