Sounds like a good plan you've got there. The weather will likely be pretty much in your favor. For free overnight accomodations with fellow cyclists, check out www.warmshowers.org. You do have to register as a potential host in Germany. Another site to check out is www.couchsurfers.com. More for non cycling tourist looking to stay a few days in one place.

Edit: This list of potential overnight spots might help, if any on your route.