Four our current address, I used my German Address, and there is a place for an address for where you plan to move. There I used my home of record.
BTW, you can only do consular processing if the U.S. Spouse has been in Germany for like six months. So, you need to keep the story straight. With that said, if you have an approval for the I-130 and they have invited you to fill out a DS-260, I would do it as soon as you can knowing it takes about 8 days to approve. Also, you will need a medical exam, and the one place that does them in Frankfurt are all booked up. You might have to go to Berlin, Hamburg, or München for that. You can also just keep checking back with their booking system to see if an appointment opens up. Here is the web address of the docs that do examinations here in Frankfurt. https://www.internisten-im-westend.de/medical-visa/ We were fortunate and got an appointment for this Thursday.