Hey mate. You're getting a lot of replies so I doubt you'll even see this. But my family commanded the Prussian armies for its entire existance and various German armies well before (and unfortunately after) that and I have LOTS of very old notes, pictures and stuff that I've been looking through over the years. I'm no historian, but I must urge you to not dig too deep into a certain area because of army affiliation. German soldiers in general where VERY fluid in their affilitations. If you were gifted soldier this is even more true. Even if a lot of people rightfully place this soldier in possibly Bavaria (my best guess too) it doesn't mean that you should dig there. He might've been born in Hamburg, met a Oldenburgian soldier that knew another in Bavaria that was looking for some good lads for a certain conflict and then he just kinda stayed.

German and Nordic family searching is probably the easiest though. We were, and still am, extremists in population administration and you have incredibly detailed records of even the lowest born peasants marriage, birth and death for as long as monks and later priests have existed in the Germanic states. North Germany/Swedish monks/priests even commonly had personal notes about every single individual in his area.

These are all publicly available and you could probably find most online. In lieu of it not existing, it might even be worth a trip to Germany. Just focus on learning the birth place of your father, then his father, then his father through this register and it should not be that difficult.

If you got the money there's plenty of German ancestry researchers that can get you detailed descriptions of your entire family for up to 15 generations back (every German could get at least 7 during WW2, hence the 7 generation german ancestry proof limit) and if you're high born, even more so. I've got a detailed family tree back to the 1000's.