NFBP

Hi @mex2lou we are receiving this same error as you. At one point we got to the second or third page (everything was super slow) but then it showed up as an error again. Maybe they are having a problem with their site? 

Since you've been living together in Germany, they will expect to see evidence of this. When my husband and I did DCF, we had a lot of documents related to co-habitation. If you click the link in my signature, you can see all the things we prepared. I believe DCF in Germany is done via mail, so you won't have a face-to-face mini interview like we did when you file the I-130.
 
During the USCIS stage (filing the I-130), everything must be translated into English, even documents in German.

Hey
1. Frankfurt does DCF so yes you are correct! You will not be needing a lawyer for this, unless she has prior convictions or overstay in the US or similar
2. I haven't done DCF specifically but when I filled out my travels while applying for K1 I believe it was by exact date - however if you don't know exactly and can't find out, fill out your very best estimate
3. Get as much evidence as possible with both of your names on it - however, I think what you should really look into here is making sure you convince them that you intend to reestablish domicile in the US, and that you will have an income once in the US. I don't think they're going to have a hard time believing you have a bonafide marriage, but they need to be convinced you're actually moving back, and that you can provide for her when you do move.

If you live in Germany and meet all the requirements that the USCIS field office in Frankfurt has, you can file DCF.
 
Check out this link and see under the I-130 section:
 
https://www.uscis.gov/about-us/find-uscis-office/international-offices/germany-frankfurt-field-office

We did DCF in Mexico.  It was very quick and easy.  We had as much as possible in both names.  We traveled internationally together so i put together a spreadsheet with our travel together.  Front load as much as you can.