We are not judging you otherwise, licenses are yours
Had I been in place of you, I would have done it in this way. First, I attached the SSD only, and removed the HDD (having power supply off from the source). Installed windows on it .
Next, disabling the power again, removed the SSD, attaching the HDD, and installed windows on it.
Now, attach back the SSD. and boot into bios settings. Set the SSD as the first boot device, and HDD as the second, cause the SSD performs well.
Due to not havint the other drive connected during installation, you will not have a dual boot. If you want to choose between your windows installations to boot up, you are to use the boot menu key .... it will list the devices available to boot from; select either the hdd or the ssd.
This one is the superior practice; coz if you have a boot menu, then in future if you want to remove either installation, there is a great possibility that bootability of the other installation will be hampered.
If anything else you want to know, let us know.