regarding wiping hdd, what i would do is
unplug PC and then detach ssd from internal power only leaving hdd attached
boot from win 10 installer
on screen after languages, choose repair this pc, not install.
choose troubleshoot
choose advanced
choose command prompt
type diskpart and press enter
type list disk and press enter
this shows all drives available, DVD/USB and hdd, make note of hdd number
type Select disk X - where X is the number of the hdd you want to wipe, change X to that number and press enter
once the drive you want to install on is chosen, type Clean
type [exit] and turn off PC
unplug PC and reattach the internal power for ssd, you can now format the hdd using disk management and set up partitons