Also, how many photos can be stored in a single photos library (this one with movies is close to 100gb)
Apple did not publish a limit to the number of a photos. But Photos is supposed to be able to open and migrate Aperture Limits. So it should be able to handle at least on million of photos and videos; that has been the limit for an Aperture library.
When I click on People to identify photos by peoples faces, it stopped after scanning only 268 of 14,000 photos.
Photos will scan your library, when you are not using Photos. Try to restart your Mac, then launch Photos to kick off the background processes and minimize Photos in the dock or quit it. Keep the Mac powered and running. The drive with the Photos Library should be connected at all times.
If you do not see any progress after a day, you may want to repair the Photos Library, see: Repair your Photos library on Mac - Apple Support
Is your library on an external drive?
Your iPhoto Library may contain image files, that Photos cannot process. iPhoto allowed to import media files, that are no ,longer supported in Photos. To check for such items, create a smart album:
- Create a new Smart Album by choosing File > New Smart Album.
- Name the Smart Album "Unable to Upload" and set the three pop-up menus to Photo - is - unable to upload to iCloud Photo Library.
- Select "Unable to Upload" in the left sidebar. If the sidebar isn't visible, choose View > Show Sidebar.
Is this album empty or are you seeing items inside?