Does anyone know from which year this upright originate? Why is Friedrich Wilhelm the Protector?

Hi, Rainmarolf!

What is the name on the fallboard of the piano, please? In case you don't know, the fallboard is the part that's right above the keys.

Thanks!

Hi again, Rainmarolf!

I hope that you return to this thread! I was really looking forward to working with you about this!

Thanks!

Having a similar piano with serial no 5550 (I'm certainly not an expert), and judging by www.piano-friedrich.de/klaviere/4.htm, I believe your piano was made in the early 1870s.