I think "in the Fredersdorf fashion" is the one that I like the most (as wording, not as a translation), although it's a bit idiosyncratic -- I suppose "in the Fredersdorf manner" is idiomatically smoother. "Soft and harsh words" is probably better in English, yes.

Yeah, either "fashion" or "manner" works for me; "way" isn't wrong, per se, but it's definitely markedly more casual. "In the Fredersdorf tradition" would also work for me.

Agree about "soft and harsh words," that's probably something I would have changed if I were polishing this up for Rheinsberg (which I intend to do if we make it through the rest of the letters--which I hope we do!).