Hard drive replaced on 2017 iMac but photos aren't showing up

Apple replaced my failed hard drive. Everything seems relatively ok except my photos. They're backed up to iCloud but weren't showing up when I clicked the Photo icon on my Mac. In addition to this, as I was running out of space on my hard drive, I now want to have my photos stored on an external SSD. I have 45,000 photos. Thought I could just drag or save them there but there was a 1,000 photo copy limit. And my albums, faces, etc. aren't appearing. I saw a msg about switching the location of the System Photo Library. I have already moved my library folder to the external drive. But a msg there says it's not searchable in Spotlight because it's not the System Photo Library. If I select "Use as System photo library" it says it will turn off iCloud photos. Any photos and videos that have not been fully downloaded will be removed from this Mac and Shared Albums will be disabled. Turn on iCloud Photos for this new System Photo Library in Settings." Since I only have 1,000 photos copied to my new photo location, I wouldn't care if I had to start over, but I want to be sure if I say ok, then I can go to Settings, and turn iCloud photos on again and the new location and iCloud will sync all of those photos with the new location.