I'm glad Kirby is Sue, she's perfect!
Ebon Moss-Bachrach already played an MCU character, he was Microchip in The Punisher. But since The Thing's gonna be mostly CGI, it doesn't really matter.
I don't know Joseph Quinn (never saw Stranger Things), be he looks the part.
I'm really not sold on Pedro tho, even with sharp fanarts (and there are a lot of very good ones), he just seems totally miscast. Besides, he's already everywhere, people have Marvel fatigue, I have Pedro fatigue.
I know the 2005/2007 movies were far from great, personally, I'm very attached to early Marvel movies. But you gotta admit, that's where the F4 cast reached its peak.