Your etymology of Dienstag and Freitag are incorrect.
Dienstag isn't Diensttag. It's probably from Proto-Germanic *þingsus dagaz, which would mean "day of Thingsus" (the Latin name of a Germanic god) according to Wiktionary.
Freitag, again according to Wiktionary, comes from Proto-Germanic *Frijjōz dagaz, "day of Frigg" (the Germanic goddess of the home).
Your other etymologies are more or less correct, but the words weren't formed from modern German words; they're much older. Montag and Sonntag are ultimately from Proto-Germanic, while Mittwoch originated in Old High German.
The serial comma is extremely rare outside of English. https://en.wikipedia.org/wiki/Serial_comma#Other_languages
Is there a historical reason why Germany doesn't have an 'Odin's Day' (Wednesday)? Although I do like the idea of calling it 'midweek'.
In low german we still have the "Wunsdag" from Wodan -> Odin.
In the 10th century christian missionaries changed the name of the day so that the memory of the 'old deities' could fade better. I don't get why they weren't interested in changing the names of the other days but maybe it's just because Odin was the main god.