A:AnswerYes, it comes with Windows. Overall its’s a great buy.
I’ve been using mine quite a lot for a few weeks with no complaints beyond the lack of number pad (which since most days I’m hooked to a keyboard, isn’t a big issue).
A:AnswerThe laptop has 2 m.2 slots, one being occupied by the 512GB intel nvme ssd that the laptop comes with, and another unoccupied slot. In my opinion yes, the wd sn750 is a good option
A:AnswerYes, on the left side of the laptop you'll find an ethernet port. You just have to pull it downward to fully open it and plug the ethernet cable right in.