Just... be careful, ok? Playing both games might mean (easily) 400 hours or more. This is THE way to get burned out on Pathfinder games. One of the factors contributing to me stopping playing WotR is that I had just finished Kingmaker back then, and it was like adding another hundred hours to the hundreds I had put in before.
I know I played Kingmaker first of course and can't imagine a situation differently, but if you're limited on time, think twice, please. WotR vs Kingmaker might be similar to BG2 vs BG1, but eventually, all their game systems improved. It's the evolution of the game developer, and the second game is more evolved (while some players might still prefer Kingmaker, it's totally fine).
But yeah, eventually Kingmaker (even all its 300 hours) felt like a tutorial for WotR, I think the second game is much more difficult and unforgiving. It would be possible to learn the systems just in WotR, but it would require really digging into all the classes, kits, races, feats, what level to pick as what class, what is the party combo, what is the balance, etc etc etc.