Wow interesting background. Best months to visit are probably June till early September. Good idea to take some time to travel through Germany. Besides of the main spots like Munich, Hamburg and Berlin, there are so many smaller places that really are hidden gems.
It´s become really easy to travel inside of Germany in the last years. There is a company called "MeinFernbus" that became really popular. It´s pretty much the same as Greyhound for example and so much cheaper and easier than travelling by train!
For me not soo many travelling plans as of now. Going to Italy for a few days on Friday, to drive around in a little Fiat 500 with my girlfriend. And then Dublin at the end of August. If I manage somehow then Amsterdam in September. Love and miss that place so much!