Warning: Users still using iPhoto considering upgrading to Catalina

If you're still using iPhoto 9.6.1 and are considering upgrading to Catalina I suggest you do the following prior to the upgrade to Catalina:

1 - run iPhoto First Aid on the library: Repair Library Permissions, Rebuild Thumbnails and Rebuild Library Database. This is to give Photos the cleanest iPhoto library to migrate.

2 - since you're on High Sierra migrate to Photos and check to see if all of your albums, projects and photos are migrated correctly. If you have problems you can open the iPhoto library with iPhoto and check its integrity and try migrating again.

Hopefully this pre-upgrade preparation will provide you with a smooth and accurate iPhoto to Photos migration.

Here are some user tips from Photos for Mac  User Tips that will help you in your transition from iPhoto to Photos:

Notes on Migrating an iPhoto Library from iPhoto to Photos for Mac

Moments in Photos are the New Events.

External Editors in Photos Are Here

Photo Editing Extensions for Photos for Mac

Post 9/30/2018 Printing Options for Photos - Apple Community

Ordering Books and Calendars on a Mac that cannot be updated past El Capitan 

Use Project Extensions to order print products in Photos after September 30, 2018 - Apple Support

Create and order print products in Photos with Project Extensions - Apple Support

Good luck with your migration and upgrade.