I may partition the SATA-SSD into either a native Windows boot version or install the deeply discounted version of Parallels that OWC sells there along with Mojave.
I¡¯m assuming that if I install a SATA 2.5¡± form factor SSD where the rotating platter drive is now, the iMac will recognize it as bootable.
Are you getting an external drive case in the package, to put your existing HDD in?
Because you could put the new SATA SSD in there, connect it up, clone your fusion drive to it, test it by trying to boot from it, and only then undertake iMac surgery to switch the drives.
And you would be left with a terabyte HDD in an external box as well.