Regarding the CG thing, I think Leffen would be able to give a much more accurate description than me. He's the one who taught me. You want to really minimize utilt use, usually I only do one, just regrab uthrow if they DI away, and regrab or uair at mid% if they don't DI, and eventually uthrow uair fsmash tipper.
On FD it's like 0~90 guaranteed, and on other stages usually you just want to keep regrabbing until they end up on the platforms, or if you're on a platform already, you try to somehow make it end with the uair fsmash or just fsmash if they DI away from the stage.
Also from under a platform , uair --> DJ on the platform uair --> fsmash is a great , great tool. No need for fancy fair stuff when you can just do that and end the stock.
About CCing stuff though : They can't do that if they're still in their teching animation, so you need to make sure to aim during those last frames where they're vulnerable, because as soon as they go back to idle position then they will CC for sure, and then yeah it won't end up good.