Moving photos from iPhoto to photo on new MacPro

It will depend on the size of your Photos library howling the " curating best photos, analyzing scenes, composing layout" will need to be completed. You can simply ignore this status message. You can use Photos before the curation is complete. This can take several weeks. Photos is doing this only in the background, when you are not using Photos, so it will not slow down your Mac when you are working with it.

Once the "curation of best photos" etc. has been completed, Photos will be able to arrange the photos better in the Days, Month, Years and present a better layout, but otherwise Photos is ready for use.

You will be seeing this status message a lot - whenever you modify your Photos Library, for example by tagging favorites or deleting or adding photos, the Photos.app may have to rearrange the the layout or look again for duplicates, etc.

You should be able to look at your pictures and edit them, but the curating may take weeks depending on the size of your library. This is hard work, especially doing face recognition and finding duplicates. But Photos won't slow down your work while you use the Photos app, so it waits until you stop using it. We generally rely on leaving it plugged in and turned on all night with Photos open and running in the background-- that is, we leave another app's window, maybe a Finder window, in front, so Photos knows we're not using it.