I definitely want to tag ISO's
Like others have suggested, it doesn't make sense to use ISO's.
Ripping to hard drive folder will allow easier playback, sidecar support, particle support, and many other advantages.
Ripping individual episodes to MKV offers even more advantages.
ISO's are for burning. Keep in mind you can convert hard drive folder rips back to ISO's very easily for whatever reason you may need them.
My suggestion for tagging ISO's:
Obviously use the Series and Season fields. Hopefully there aren't multiple seasons on one disk.
For the episode field you can list the episode on each disc. ie "01-04" for disc 1, "05-08" for disc 2, etc.
Typically you can get the episodes from the dvd case.
You cannot scrape for episode info. All tags will be in the library only so be care if you more the ISO's.
Cover art may not show up properly by default because ISO's are data but it's not hard to make it.