Need help getting into the game side of the hobby...

So to preface, I like many others, during the COVID lockdown spent a fair amount on minis, codex, kill team box, etc. I was having fun doing the painting side but I never got around to playing the actual game , which was the ultimate end goal. Unfortunately, after the lockdown, I didn't have nearly as much time to put into the hobby anymore, and now I'm left with some outdated rules and whatnot. To be specific, I currently have the Octarius Kill Team box ( which I'm currently finishing up to try first before proper 40k), and about 500 points each of Black Templars (army set) and Death Guard (various boxes: Plague Marines, BL Terminators, Lord of Viru, Lord of Contagion, and Myphitic Blight-hauler), as well as their respective codex for 9th edtion. Im just missing the 9th edition Core Rule book and the Space Marine codex for 9th. So my question is, should I just grab those 2 books I'm missing since they are dirt cheap currently to try the game to see if I even like it or should I just go for the 10th edition books for everything? The same kind of applies for Kill Team since that version is now old as well. My only concern is if i just play 9th edition to try the game out, where can I find the last version of the Munitorum Field Guide for 9th edtion? I'd appreciate any help at all and I'm super excited to try the game with some buddies