As for integrating those online streaming platforms, you’re probably out of luck as those aren’t particularly fond of having their catalogs/content integrated in anything but their own apps.
Also, Plex has recently updated their remarks about feature requests and indicated they will no longer accept feature suggestions asking to integrate provider XYZ → Please Read: Before submitting a feature Suggestion
As for getting links to various online streaming providers… this has been implemented for Plex’ own video on-demand service (via https://watch.plex.tv). This page is showing a much wider catalog than what’s actually available on Plex – for items not available through Plex, they’re now listing alternative streaming platforms which should be available from your region.
While this doesn’t cover your personal library it’s still pretty cool/useful