I just checked some of them out and honestly, the handwriting is rather neat compared to other stuff I've had to decipher :D As long as there's not too much bleeding from the ink on the letter in question (like on the Dresden one, that one would have been quite tiresome to work through), I could probably manage to transcribe it. Unless Fritz only used his neater handwriting for Wilhelmine, but facsimiles of other stuff I've seen look similar enough.

This is impressive!
Thank you ^^' I've only transcribed a few of the older types of writing in a class I took in my first semester at uni (back in the good old days of actually BEING at uni) and learned a little bit about them, so I'm no expert by any means. Though I did really enjoy this class (and auxiliary sciences as a whole), so I'm glad it might be of use :D

Late 19th/early 20th century German cursive is something I'm a little better at (taught myself how to write in it some years ago for this exact purpose with the added bonus of being able to write whatever I want in class without people being able to read it), and I feel like that's helping me quite a bit with this :D