If it's not an RTS then I'm down to play it for sure. From what I've read online CK3 has a streamlined UI, without dumbing the series down. Since CK2 is free I'll try that as well. Do those CK2 DLC packs ever go on sale? $300 seems like a lot of money for DLC IMO.
You should be good then. It's technically an RTS with pause, but in this case 'with pause' means 'play at your own pace'. In CK2, I think you can even configure what events pause the game automatically. As for CK2 DLC, they go on sale constantly. I don't think the prices are that great even when discounted, but discount percentages aren't horrible either, so as long as you know what to expect pricing-wise, you should be good.