I'm not sure you really need to, as the only relevant thing that's relevant in the first Witcher is they lean heavily into Geralt's amnesia, and, if you play it that way, how Geralt's and Triss' romance really goes into full gear. It deals very little with the Wild Hunt (only instances in the first act and the final boss fight) and it seems like everyone in the game knows you, but because of the amnesia you have no idea why - and they go very little into it. That, and the Scoiatel aren't necessarily the enemy - only if your choices lead them to be. Yennifer isn't even mentioned by name and is only even hinted at once or twice.
I'm not saying it's bad, it's actually quite good. It's just completely unnecessary to play when trying to understand what's going on in 2 and 3. I'd say 2 is probably much more important to 3 than 1 is to either of them. But if you're a fan of the series, then get it and play it. But I'll also agree with a lot of comments online - it really needs to be remastered. It probably looks good compared to a typical 2006 game, but compared to Witcher 2 and 3 the character models are awful. Triss looks so bad they remodeled her for 2 (which carried over to 3). At least they carried over Shani's character model over to 3.