Joseph Walker has a very interesting dilemma:
My 1TB iMac died and I decided I wanted to move 400GB of photos and videos into the iCloud Photo Library and enjoy all the syncing features along with simplified backup protection. I purchased a 128GB SSD MacBook Pro. I cannot figure out any way to take three 100GB+ photo libraries and get them into the cloud library??
Joseph suggested a number of strategies he’d thought of, and discarded for various reasons. However, I’ve got an answer for him that he might actually like. Joseph is perfectly happy to pay for the cloud storage to keep iCloud Photo Library his master copy.