You can, but it requires you to set up and install additional software manually, since Plex doesn’t read Kodi’s .nfo files by default. .nfo importer agents
No Wake-On-Lan
Sorry, I cannot answer any of the RasPi-specific questions.
Keep in mind though, that the RasPi is not an adequate hardware for using all of Plex’s features.
You’ll have to compromise and manually prepare/convert your media files to avoid transcoding at all costs.
Pi 4 handle plex, yes but only if you are not transcoding. The pi cannot realistically handle transcoding. If you are direct playing, I’ve seen my pi 3 handle 3 streams at once without an issue. A single transcoding stream kills it, buffers constantly and unusable.