Pretty much all Germans learn English in school. But not all folks here are good at it or are locals. My ex from the States, who only knew English when she came here had bigger problems than I ever expected. But, as anywhere, if you give it some effort and use hands and feet people will try to help.
Never been to Hessen or Osnabrück, so can't comment. Munich is nice though there's a local tradition for being grumpy. I'm living there again. We got over 1000 beergardens [http://en.wikipedia.org/wiki/Beer_garden] in and around town, where you can sit outside, shaded by trees, drink beer in 1 litre mugs [http://en.wikipedia.org/wiki/Ma%C3%9F] (2 pints) and buy or bring your own food. And there's the Oktoberfest of course. Ah, and I think the nude sun bathing here is pretty well known.
I also found the region around the Rhine river pretty impressive. With, at some places like Koblenz [http://en.wikipedia.org/wiki/Koblenz], all them castles but a few miles apart. There's lots of wine farming, too, with fun town celebrations after the harvest to have some tastings.
Hope you'll enjoy your stay.
(and while it is true about German punctuality and doing things by the book, following the rules, I sure don't fit that description)