Especially the shoulder guard looks really stupid. there are simply no matching pieces.
They do have one single matching piece, and they go along really well in my opinion. And the latest patch that gave the nobles and some of the units different/more armour pieces did a good job in my opinion.
But I still think aesthetic wise there's more to be done, simple things such as alternative versions of the northern mail that gives different colours on the pants instead of just white/red, some examples being: green/brown, red/gold, blue/gold, blue/white. There should also be colour variations on that new shoulder piece that was added, and others.
The "brass shoulderpads" or whatever they're called are just straight out of a fantasy game, in my opinion just remove them

The "northern warlord helmet" is probably the ugliest helmet in the game, and also happens to be the best one, and also happens to be used by sea raiders for some reason. Honestly just nerf it, it doesn't even look functionally the best.
TLDR: More armour pieces, more colour variants of the same pieces. More cloth and more furs.
I'm biased regarding my opinions about how much influence from what historical peoples Sturgia should have, mostly because I'm just so tired of seeing vikings everywhere for the past 20 years in video games and movies, Slavic inspiration and aesthetics is such a refreshing change. But the faction and its lore is what it is, and the sources for its inspiration aswell, so I think that having access to recruits from the Skolderbrotva would be the single best way to achieve what you write about.
It would also lorewise make the most sense, I'll explain why: While it does seem like some Nords have moved into Sturgian lands (a few notables spawn with Norse names as opposed to Slavic ones), I don't think the presence warrants an easily accessible Nord troop tree (not saying you said that), and the factions lore is that the most Nord involvment with Sturgia so far has been through mercenaries as opposed to anything else, so when we do have a literal Nord mercenary company as a minor faction within Sturgia, I think we should make use of that.
I think further down the early access development line as the main factions interactions with their minor factions grows, we'll probably see that happen, hopefully atleast.
Also: Raganvads mother is stated to be a Nord with ties to the Skolderbrotva company, so almost exactly like you wrote, the lore is all there already, we just need to be given access to Skolderbrotva recruits someway.
Sturgia Rework mod
https://www.nexusmods.com/mountandblade2bannerlord/mods/547
"This is a Rework of the Sturgian Troop Tree.
I played them and somehow the Sturgian Troops felt a bit weird. The Spearman was absolute crap with just T3 equipment as T4 unit and the Ulfhednar looses almost all armor, etc.
So I wanted to balance them a little bit.
This is my first mod.
Feedback is always welcome. "
I have seen your mod, so far most modders are doing a very good job with makeshift balancing and you're no exception, good job but I prefer to play with stat-fixing mods so far

I like staying as true to the intended vanilla design as possible.
Well, we can change stats aswell, so why not change the stats? I don't see why we would have to be locked into balancing units a certain way because their stats are currently in a certain way.
Besides fixing stats and fixing equipment (i.e buffing), I can summarize in my opinon what Sturgia needs with this:
- The Lords need to fight on foot with their infantry in order to not be too exposed, or if more cavalry is introduced, they can continue fighting on horseback.
- If cavalry is made available through the basic troop tree line, then the Lords should continue fighting on horseback, and if that is done, then the Druzhinnik needs to be turned into a very strong infantry unit, otherwise Sturgia would become too cavalry-heavy (this is an opinion and not necessarily a point regarding balance).
- If cavalry is not made available through the basic troop tree line, then Druzhinnik
still needs to be turned into a very strong infantry unit, but the Lords need to start fighting on foot with the infantry,
otherwise they'd be too exposed. Not to mention that the Druzhinniks
would be too exposed aswell as they are right now as the sole melee cavalry unit of Sturgia, they're simply too few in numbers and just straight up die all the time.
- Ulfhednar/Shock Troop needs to be combined into a new proper 2H+1H+THROW+SHIELD unit with actual good armour and stats. Currently there's literally no reason to recruit either of them,
because both are lacking in the department where they need to be good. If the final basic troop tree infantry choice stands between: Standard heavy infantry with very good 1H and Throwing VS Shock heavy infantry with very good 2H and Athlethics then that is an actual meaningful choice, as opposed to the current choice between three units, of which two are lackluster compared to the veteran warrior.
I didn't take autocalculation bonuses into consideration, but since not every faction has every sort of unit (I don't think Vlandia or Battania have horse archers) I don't think it's a necessity for Sturgia to have one either, although it would make sense considering their proximity to the Khuzaits. But if the choice is between Horse Archer and regular Cavalry, I'd give Sturgia regular cavalry. A solution of course could be to split the final line of a cavalry line into a horse archer and a regular cavalry unit.