Can't give much advice on the places mentioned but Bamberg in Northern Bavaria is a really really nice spot with some excellent beer and sort of on your way! Home of Schlenkerla and a few other great breweries!
Rauchbier straight from cask! Some breweries (Speizal and Mahr's anyway) do a really nice ungetspundet (unfiltered and unpasteurised hazy lager).
I think Bamberg has the most breweries per capita on the world aswell! It's one of the few places that wasn't touched in the war aswell so has all that old school German charm!
A potential stop off between frankfurt and lepzeig, but might be a bit out of the way!
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