My lunchbreak is ending, so I can work on this with you in more detail later, but here are my initial thoughts:
Basically any civilized society that exists currently is roughly sixty years old at the most. Is that enough time for this empire to have sprung up and established all of these customs?
Borea is mostly temperate. If you couldn't tell by the shitty map, it's basically Europe. As you go North into Hyperborea and Lemuria, it becomes more of a Tundra, and eventually Arctic. This is probably important to note if you want to write about a society of Northmen.
What you've written I think would probably work best as some sort of derivative of Lemurians more than Thule or Hyperboreans. Think of Lemuria as somewhere between Russia and Monoglia; it's a vast, cold, shitty plains. The Lemurian tribes were united under a single warlord during the Years of Dusk, but he died and his empire dissolved before the Age of Dawn began. Perhaps this lends some inspiration to you.
The Thalzamarian Empire was very heavily inspired by Imperial Russia, with a bit of Japanese culture thrown in, so setting it near the Lemurians would make sense, if you're okay with that.
What I had planned is that when the remaining Hyperboreans (substituted for Lemurians now) and Khalaevna invade Thalzamaria, their military is spread too thinly across the kingdom, and by the time they're able to formulate a response the capitals already been sacked and the Tsar and the royal family has been butchered. The noble Thalzamarians would then form a sort of pact with the Lemurians, where the empire is dissolved, and reforms as a new kingdom which combines Thalzamaria and the Lemurians.
Khalaevna marries Carthain, then has him assassinated and becomes the absolute monarch.
Does that fit in with your ideas, at all?
