Probably, yes.

For me, Total War: Warhammer 2 is one of the best strategy games ever made. It has so many unique factions and playstyles that it is hard not to find one you like and plenty of mods to change things up, from ui changes all the way to new factions to play. Whereas I find the historical titles a little bland due to every faction having the same core with a few unique units thrown in, TW:W2 has clearly defined races with different leaders that add all sorts of buffs and bonuses to their factions/armies.

Find a faction you find interesting and play one of the base lords first. You don't have to finish the campaign but take it until you get a good feel for the faction. If you like how it plays, check out the DLC Lord packs. For the 4 fully DLC factions, check out some gameplay vids.

"How necessary is the DLC?" - Not. You can play the base game and it's great. Download all the free DLC. The paid DLCs add Content, unlike many strategy games where they really add Features. This is not like Civ where you need an expansion to add espionage and one to add religion and so forth. The main game mechanics are there for four factions. If you don't want to play as the Vampire Coast, don't buy that DLC. If you don't want to play as the Tomb Kings, don't buy that DLC. The game is definitely not incomplete without the paid DLC.

"Is it worth it?" - Almost always yes. Once you've played a few campaigns with the base factions, you'll discover how differently each faction plays from others - hell even how differently each Lord plays within the same faction. If you're anything like me, you'll want to try Tomb Kings, and Vampire Coast, and Ikit Claw and Markus Wulfhart and and and. Over time, I eventually bought all the DLC for TWW2 and I was happy to do so. Each one I felt I got my money's worth, but the key is over time. I didn't buy all of them up front, because there's basically no point to doing so. Owning the Vampire Coast DLC doesn't change your High Elf play through. Wait for a sale, or for when you're itching to play something specific.

"Should I wait for TWW3?" - Almost certainly no. With TWW1 and TWW2, it's not "the old game" and then "the same content updated to the new game". It's completely separate content. TWW1 is the Old World map and campaign, with the Old World factions (Empire, Dwarfs, Greenskins, Vampire Counts). TWW2 is the New World map with Vortex Campaign and new factions (High Elf, Dark Elf, Skaven, Lizardmen). Buying TWW2 doesn't give you Dwarfs or VCs or Greenskins. Here's the twist - owing both games lets you merge the maps and races together, so you can play any of the Old World races now on the "Mortal Empires" map which consolidates both games. I would be surprised if TWW3 doesn't do something similar. So IOW, owning TWW2 when TWW3 comes out won't be money wasted - it will likely represent more content accessible in the future game.