You have a lot of model lines to choose from for Varangrr these days, and I’d say it depends on how much you want to spend, what you want the army comp to look like (lots of different kinds of infantry? lots of knights? lots of large infantry / monsters?), and most importantly what models do you want to paint / push around.
A great many Varangur armies in 2E were converted over from WHFB Chaos Warrior armies, which is fine and cool. You’ll primarily want to use eBay and used sources if you want to recreate this look, as many of these kits aren’t supported by GW any longer, or if they are, then they’re selling reboxed ancient kits for $$$ (like the old chaos warrior plastics). In which case aftermarket is best. Going this ‘old chaos’ route also lets you use loads of OOP Chaos models, if that appeals to you.
GW has finally updated the mortals part of their Chaos ranges, from the basic ‘Chaos Warrior’ (now called Slaves to Darkness and/or Darkoth stuff) to the Tizz mortals to the upcoming Slaanesh mortals. If you want to spend $$$, these would make for some awesome armies. Personally, I’d lean heavily on the Start Collecting S2D set (https://www.games-workshop.com/en-US/Start-Collecting-Slaves-To-Darkness-2019?_requestid=8265104) as the savings are decent and all those models are usable and good in KOW. It’ll be super elite, but that’s basically 1 Huscarls regiment + 1 Knights regiment + 1 Hero on Frostfang. Or a whole unit of Frostfang if you bought 3 O_O Toss in some Fenrisian Wolf kits for wolf troops and you’re actually on your way to something!
Mantic is absolutely an option as well, and will be far cheaper if not as visibly EEEVIL as the S2D option. I also think this is the better option if you’re looking to run a lot of Draugr, as the Mantic zombies are very good and the GW ones are horrible. (I’d say … converted poxwalkers?? if you wanted to go full GW and use Draugr.) Pretty sure there isn’t a Mantic option for Varangrr Knights though, so this is more an infantry + frostfang hammer sort of list … which you could basically do with Northern Alliance, as knights are the Varangrr thing.
From here, you can start exploring the wide range of not-Chaos made by other companies. Avatars of War made a few Chaos Warrior infantry kits that are mostly available and mostly solid (https://www.chaosorc.com/product_info.php?products_id=24029)(https://www.chaosorc.com/product_info.php?products_id=24030)(https://www.chaosorc.com/product_info.php?products_id=27068)(https://www.chaosorc.com/product_info.php?products_id=26528). Loads of heroes too. Then if you really want to spend money, Mierce (https://www.mierce-miniatures.com/) makes infantry as well as amazing monsters … but you’re more likely to use the large infantry and monsters from them, simply for $$ reasons. They have quite a few sales if those prices look scary.
Anyway, that was a lot. I’m sure Varangur groups have ready made lists of minis if you want them, and like I said, a lot hinges on how much you want to spend and what overall look and feel you’re going for. It sounds like you’re most familiar with GW, and I do think the S2D starter box angle is a concept. Here’s a quick example of how off-the-shelf GW S2D might convert to KOW:
Army: Varangur
Points: 2000
Unit Count: 11
Unit Strength: 21
265, Frostfang Cavalry Horde
245, Mounted Sons of Korgaan Regiment
– Maccwar’s Potion of the Caterpillar
– Guise of the Deceiver
225, Mounted Sons of Korgaan Regiment
– Guise of the Deceiver
225, Huscarl Regiment
225, Huscarl Regiment
225, Huscarl Regiment
115, Tundra Wolf Troop
115, Tundra Wolf Troop
115, Tundra Wolf Troop
110, Lord
135, Magus
– Inspiring Talisman
– Horse
That’s 3x Getting Started S2D (3x Karkadrak = Frostfangs, (2x) 7x Knights = Mounted Sons, (3x) 10x Warriors = Huscarls), either a bunch of Dire Wolves or Fenrisian Wolves (12ish), a Chaos Lord or Darkoth hero if you prefer, and you could probably convert a leftover knight into a mounted Magus, as there aren’t a lot of modern GW options. Chaos Warrior wizards aren’t wizened old milksops anyway, so it checks out and will fit with the mounted dudes he’s riding along beside.
^ This isn’t an amazing list, but it’s extremely smashy and tough enough to get there in most cases. It’s also a decent start to begin learning the game, especially how to use chaff, that you can expand from with some War Cry warbands or whatever new Chaos stuff you like the look of. And maybe you try to jam Archaon onto a 75mm for your King on Chimera 
