Can I have my Windows OS in my main disk and also Zorin OS on another external drive?
Yes you can. When you have your pendrive with installation live Zorin after installation you can choose which one hard disk it will be installed.
More simple if this is laptop or a desktop pc. You can unmount original primary hard disk and then you can directly installing Zorin on external hard disk. Tutorial with partition is somewhere on this forum. Why unmount original hard disk?
Sometimes people choose wrong options and lost many data files.
Does it show if it's an SSD or a HDD or some nvme drive? or does it have any sort of differentiating between them?
And what installation option should I choose?
Here is some guide
but every user can decide how he can want using a partitioning.
Thanks! Now i gotta get some cash for a drive though...