Although this isn’t quite relevant before finishing the main game, be sure to pick up both the DLC once you’re finished.
Both DLCs are fantastic standalone stories, super rich in content they could even beat some full priced games. You could play the DLCs before finishing the main game (and there is an additional game mechanic introduced in Blood and Wine), but on a first run I would still recommend playing it after to not get distracted and take away the impact of the main story.