When choosing the institute as a Phd candidate, what aspects should be considered? (In Germany)
Of course, as you said, your academic interests are important. And your advisor is also important: there is (in all places I know) no academic training "how to supervise" whatsoever - there are extremly bad advisors and very good ones. If you know something about the prospective advisors, take this into account. 
Of course, some advisors are good for some students and bad for others. As you want to go to industry, it could be nice not to have one of the "industry is evil"-type of advisors (if they are common or not is field-dependent). 

Having a good advisors is really important, especially in Germany the situation is really hierarchical and if your advisor is mean to you, you cannot efficiently complain about them.

Otherwise, pick a place where you can imagine to live in. And, it goes without saying, if you have a partner (and/or kids, or family you have to take care of) take their opinions absolutely into account! Having a good PhD position but a bad private life happens unfortunately very often to academics.