32gig for os is pretty small, especially if you intend to run windows. windows alone will gobble that up and leave you nothing. linux may use less space, but still 32g is cramped.
64, or 128g would be a better, safer, system disk.
plex stores files in 2 places, the binaries/executables are typically stored on the system disk, on windows you set the install location for these files, but on linux there isn’t a supported way to change install location.
plex data is stored in a different set of folders (separate from the executables).
the plex data is more easily moved to alternate locations.
generally the program files is maybe a couple hundred megs, but the data folders can be several gigs to hundreds of gigs in size.
there are more details on where plex stores the files in the support docs @ https://support.plex.tv/articles/?s=Data+directory+&search=support_articles
these threads may also be of use:
all about 4k transcoding @ Plex, 4k, transcoding, and you
