On my almost-stock (primarily used for iOS deployment) MBP, Catalina uses 3GB RAM (active+wired) memory on boot. It's much more than my Linux laptop (~400MB). I haven't booted Win10 recently but I'd assume it'd be close to macOS.

The transfer speeds of the M1 SSDs have been benched at 2.7GB/s - about the same speed as mid-range NVMe SSDs (my ADATA SX8200 Pro and Sabrent Rocket are both faster and go for about $120/TB).