If you've managed to grab Total War: Warhammer and its sequel during the most recent Sega sale, you might be interested to hear that their DLCs are now all at 50% discount on Steam - the lowest they have ever been. And yes, this applies to Norsca as well, though the savage Northerners will not be available in Total War: Warhammer 2 until May.
Speaking of which, it is also important to mention that all of the DLC applies to both Total War: Warhammer 1 and 2. So if you want to play as Norsca, feel free to buy them as you'll be able to mess around with them in Total War: Warhammer 1 right now, and then just start up a new playthrough once they finally become available in Total War: Warhammer 2 as well. Not a bad deal, all things considered.
If you're not familiar with all of the DLC and you're currently wondering what's even worth grabbing, I would say that Norsca and The King and the Warlord are the only two 'must-haves'. Norsca has one of the best unit rosters and campaign mechanics, so regardless of your playstyle they are a great addition as they really do offer an interesting take on the standard Total War gameplay.
On the other hand, The King and the Warlord DLC only adds a couple of units, but what it does offer is a truly unique starting position with some really tricky restrictions. You're probably going to get crushed during your first playthrough or two, but once you get used to the rather strange circumstances chances are you'll find it to be a refreshing change from the usual Greenskins/Dwarf gameplay.
As for the rest, it's pretty much up to you and your preferences. I love giant monsters and in-your-face tactics so the Beastmen were an easy purchase, but you might be more of a fan of defensive playstyles in which case the Wood Elves are far superior, though they do require significantly more attention and micromanagement in order to succeed. There is simply no way for me to recommend one over the other, or even over the somewhat unfinished Chaos Warriors, so I would highly recommend you do a bit more research before diving in. Have fun!