You should not have to buy a new key for a machine that came with windows. That will most likely automatically activate back to whichever edition you had before the wipe.

They’re just trying to be fancy when writing 40-70% for the advertisement.

A Surface might do, unless you find that to be too big for your liking.

It’s programming languages all the way down.

Systemd basically is what starts up other processes. You don’t need systemd, but you do need some init manager. Kernel loads, then calls up the init manager to load everything else. Anything you want to make run on startup gets added to the init manager.