A nice piece you got there....
"Mit Gott für König und Vaterland!" means as you already found out "With God for King and native country!"
Suum Cuique means in German "Jedem das Seine!" or in English "To each his own", but with idiomatic meaning of "to each according to his/her merits".
The star is known as the
Order of the Black Eagle (German: Schwarzer-Adler-Orden) and was the highest order of chivalry in Prussia or is also known as the guard-star (Gardestern).
It is today still the symbol of the military police (Feldjäger) of the Bundeswehr.
In your case the eagle and the star belong together.
It the so called Garde-Adler (guard eagle). The photo shows the version for officer rank, yours is the version for crew ranks because the star is silver.
It was worn by the soldiers of the Gardekorps (guard corps).
The guard corps was arranged, after the last peace conditions from 1914, into 2 guard infantry divisions with 5 guard infantry brigades, a guard chivalry division with 4 guard chivalry brigades, 2 guard field artillery brigades, a railway brigade and other troops and authorities.
Commanding Officer of the two elite guard regiments, the first guard regiment to foot and the regiment Gardes du Corps was always the respective king of Prussia.