Welcome to Plex.
A few considerations…
Disc images / ISO files
Plex won’t deal with your disc images (e.g. ISO files). The common approach within Plex is to add other media from your discs as Local Extras to the main movie. This should give you a more linear user experience.
https://support.plex.tv/articles/201426506-why-are-iso-video-ts-and-other-disk-image-formats-not-supported/
https://support.plex.tv/articles/local-files-for-trailers-and-extras/
Genre Organization
The “idea” in Plex is to use the user front end to navigate your media. Plex will e.g. add genre information from its online sources and let you filter / navigate your library by those parameters (genres, collections, actors, directors…). It’s possible to navigate your library “by folders” but that’s quite limited.
For movies it’s easy to keep those folders – e.g. to find your media in Explorer.
For TV show based content, Plex is quite adamant to find your media in accordance with their naming schema… otherwise it might not be able to match it (or not show it at all).
As an example:
If you want to keep your genre based folder structure for TV Shows, make sure to add each genre folder individually to your Plex library (each library can have multiple top-level folders assigned as long as the media is properly organized inside those top-level folders!) – those folders linked to a library can also be spread over different drives.
P:\
Sci-Fi <- Folder linked to your Plex TV Show library
Foundation (2021)
Season 01
Foundation (2021) - s01e01 - The Emperor's Peace.mkv
Foundation (2021) - s01e02.mkv <- Plex isn't using the episode title from the file name... so this can easily be dropped/ignored
...
Foundation (2021) - s01e10 - The Leap.mkv
The same applies to Battlestar Galactica. Keep in mind that Plex is defaulting to The Movie Database when it comes to episode ordering – and their episode ordering is quite different from that you can find on IMDb or TheTVDb. That makes it more of a project to get the order right (or find the order you like).
Here’s a thread where this mismatch has been discussed in more detail. To be fair… this is more of an exception
