You get the same types of choices that you get in the first two games, but it’s really streamlined. And you can absolutely murder/spare people as you see fit because it doesn’t really affect the outcome. There is an achievement for clearing a single level without killing anyone, but not one for the whole game.
I didn’t even realize there wasn’t a chaos system until I finished the first level. I still played my usual way on that first playthrough, though (ghost/clean hands). On the second run I murdered everyone. Third run was the Original Game+ (where you get to use some of Corvo’s and Emily’s powers instead of your own)… that one was actually the hardest because Billie’s powers are honestly better, at least in this one.
The only thing I’ve never really done in these games is go with the combat-- I’m purely stealth. I know the combat is amazing and completely open-ended, but I honestly suck at it.
I’d definitely take the opportunity to make sure the BIOS is up to date (just to be sure you’re running one that supports the newer CPU), or just default everything if you’re already on the current version before pulling the 5600G and dropping the new one in. Then after you’ve confirmed the board recognizes the 5700X3D it’s just a matter of changing your settings back and dialing in the memory timings.
I know it’s tedious, and probably not strictly necessary, but I figure it’s better to start off with a clean slate whenever you swap out a CPU or reconfigure your memory, just so something you didn’t think about doesn’t come back to bite you later on.
I usually just go through all the BIOS screens where I’ve made changes and take photos with my phone, then use those as cheat sheets to refer back to.