score:1
I finally got the answer, not by research but from my friend. The person was:
Johann Wilhelm von Archenholz
He served as a company commander in the Seven Years' War. He was discharged from the army after being badly wounded in this war.
He has been a member of the Masonic lodge since the mid-1760s.
He fell off a horse in Rome in 1780, and one foot was permanently paralyzed.
He was threatened with guillotine in France and therefore left France and settled in Hamburg. Meanwhile, he wrote a book about the life of Gustav I of Sweden. (4th and 6th tips)
His writings about Felice Peretti di Montalto (Pope Sixtus V) are collected in the book 'Kleine historische Schriften' with adding 3 other titles. (This is not the book mentioned in the 4th tip :) )
He lived in Hamburg until his death, and in Hamburg there is a street (ArchenholzstraΓe) named after his surname.
His most famous book 'England und Italie' made a huge impact in Europe. In the book, he compared the political situation of both countries and belittled Italy against England. Goethe harshly criticized this condescending attitude at that time.
Upvote:3
Count J. A. Huebner roughly matches your description.
HΓΌbner wrote both a famous book about Sixtus V and a famous memoir on Italian politics. He was not in the military but he was a diplomat. In his youth he worked for the Austrian intelligence. I don't know if he was ever wounded or threatened but in 1848 he was held hostage by the Milanese revolutionary government. He never spent a lot of time in one place, though, travelling extensively both on diplomatic missions and for his own pleasure. He died in Vienna. I couldn't find any better candidate.