

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.
You should be able to sign in to just the store app by clicking a tiny little box on the subsequent window that pops up during the sign-in process. That’s how I sign in to the store for app downloads without having to use those same credentials to sign in to the PC.
That box is intentionally made small and easy to miss because they obviously want you to use a MS account across the whole machine, but it’s there if you move slowly and look for it.
That said, you shouldn’t have to sign in to download any app updates from the store. You can also download new apps without signing in-- the license will just be tied to the machine instead of your personal account if you do that.
This unhelpful error is just MS being MS. Best option is usually just to leave it be and check back later, as it oftentimes really is a problem on their end.