Adding '-ing' to masculine nouns doesn't automatically make them feminine in Old Norse, so words like 'Keisaring', 'Stórrhertoging', 'Hertoging' etc. aren't grammatically correct.
I really disagree with using 'Hertogi' or 'Stórrhertogi' in Old Norse for a duchy-tier title. 'Hertogi' in Old Norse is either derived from Proto-Germanic 'harjatugô', literally meaning 'army-leader'. Or, it's potentially a late-13th century borrowing from Middle Low German 'hertoch', which is derived from the same root; however, by the 13th century it acquired the feudal meaning of 'duke' in the Holy Roman Empire due to it being used to translate Latin 'dux'. Either way, it wouldn't be used to refer to a territorial feudal duke in 9th century or even 11th century Scandinavia. If anything, it would be used to refer to generals and commanders of a Norse 'herr' (army).
'Riddari', likewise, is definitely a 13th-century borrowing from Middle Low German 'ridder', meaning 'rider' i.e. a knight, but wouldn't be used to refer to a Norse warrior in 867 or 1066 AD. A more appropriate term would be 'húskarl' or 'þegn'.
I'd use 'hersir' instead of 'þegn' for the baron-tier title in Old Norse. A 'hersir' in Viking Age Scandinavia was a local chief of a 'herað' (administrative district roughly comprising 120 households).
For Old Norse, my suggestions would be:
Emperor - Keisari
King - Þjóðkonungr (Gyða uses this title in Heimskringla to describe King Gormr of Denmark and King Eiríkr of Sweden when she rejects Haraldr Fairhair because he 'is only king over a few districts')
Petty king/independent duke/independent count - Konungr
Vassal duke/high chief - Jarl
Vassal count/chief - Hǫfðingi
Vassal baron - Hersir
Vassal temple-holder - Goði
Queen - Dróttning
Prince - Ǫðlingr
Princess - Dróttning (wives and daughters of kings were both called this)
Knight - Húskarl or Þegn
Commander - Hertogi or Foringi
Marshal - Stallari
Steward - Bryti
Chancellor - Dróttseti
Spymaster - Spæjari
Court Chaplain - Dróttgoði