I don't see why a 2 or a 3 would hurt you: the university probably would just ignore that and simply not provide you placement for that subject, unless you prove otherwise that you deserve it.
This table might be useful to help you know what courses AP scores will place you into:
Princeton - About Advanced Placement and Advanced Standing
From what I hear, the departments sound quite flexible, and if you tell the department that you are definitely qualified for a certain level course, they may give you the benefit of the doubt: it's unlikely that someone will stick with a class they're clearly unqualified for, anyway. For history courses it just says "departmental permission required." For German, an AP score of 4 places you into 200-level courses. GER 210 - Introduction to German Philosophy is clearly a 200-level course, so I believe you could take that with an AP 4. I'm not sure what the department will suggest you do, of course, but even if they recommend you against it, if you're adamant I'm sure you're fine taking it.