do i just go to settings > recovery > restart this pc > remove everything > remove files and clean drive > reset

and if I follow all of those steps it'll just be off my hdd?

then i switch to ssd hardware and boot from usb to install windows 10

just remove drive put in ssd and install windows, when you reconnect drive format it.

so the windows will be fine on 2 different drives? wont when I install the ssd it'll say the key is being used atm?

pc only boots 1 drive at a time.

technically could I just ditch my old drive?

yeah you could but theres no real reason to, its just free storage. when you connect it and its isnt your boot drive just reformat it if you dont need anything on it. Free storage space is free storage space ya know?