Is there any need to move data over?
I assume that plex stores some data about where the libraries are in the user profile (really should ether be in teh public folder or some other non-user specific location)
or does plex atleast do that as is?
These questions are general Plex Media Server questions and it running a Service has no bearing
1. The media files (movies / home videos / music / photos / tv shows) need to be accessible to the new user account but do not have to be stored in the user's local area.
If you decide to move the media files or access them in a different way (eg switch from mapped drive to unc), then follow the instructions here:
2. If you have an existing Plex Media Server installation you want to migrate all the meta data collected and used by Plex Media Server and the database contents to a different account then have a look at this Support page
https://plexapp.zendesk.com/hc/en-us/articles/201370363-Moving-a-Database-from-one-Server-to-another
3. Whenever Plex Media Server starts for the first time in a user account, it will create the local data area if it does not exist - otherwise it will use the existing data
