Greetings Everyone. I have posted several times in this thread and thought I'd give an update (my last unless I discover something new). As of today, I have now been running the Photos program for a total of around 72 hours and iCloud for around 40 hours. Not continuously, but for long continuous time periods (10 hours, 24 hours, 20 hours, 22 hours). For a lot of that time I also let iCloud run on the computer. I let NO other programs run (WARNING: Mail does not "play well" with Photos, at least in this uploading stage. Mail runs slow and has crashed several times). In the beginning of the photograph uploading you can following the uploading of pictures on iCloud. At the bottom of the iCloud > Photos, on the screen it gives you a photo upload count roughly every 20 - 30 seconds. These updates stop after 5 minutes, then you have mouse click your browser's REFRESH button, and the counter will run for another 5 minutes. At least that way you can see if your photos are being updated. I was loading around 700 - 800 photos per hour at a rate of around 1Mbps (I have FIOS and should have gotten better upload speeds, but did not). I had 28,000 photos, the process took over 30 hours just to upload the photos. (NOTE: once you have over 20K photos, it takes the computer a LONG time to count the photos (30-60 seconds!).
HOWEVER -- that is not all that Photos is doing. At the same time it appears to be building and/or activating the Photos software. At first I could not edit any photos, then later I could use Rotate, Crop and Filters -- but none of the other 6 features. Still later in the process I could use Enhance and some of the Adjust features. Now, I can use ALL of the Edit features.
Also, the longer you let Photos and iCloud run, the more "stuff" gets uploaded to iCloud AND appears in Photos. At first I was just getting photographs in iCloud > Photos. Later, in Photos, I started to get SOME events and SOME projects, in iCloud is had SOME Albums. At first, the events I got did not have the iPhoto name nor did it contain all the photos in that event. Eventually the event names populated the folders, as did the photos. Now, I have almost all the events on iCloud and in Photos (and all the projects in Photos). iCloud and Photos both store you photos by date taken (kind of like all the events you made, but photos are now in individual folders labeled by date, and the SAME photos are also in another group of folders arranged by event name). It looks to me that full photographs were integrated first, then the thumbnails were uploaded later (or repopulated from the iCloud storage by Photos?). I'm not sure of HOW this is all working, I can just relay what I am seeing.
Even after 72 hours of running iCloud and Photos, it is still NOT finished. I am getting close but both iCloud and Photos STILL have events to fill in with photos.
Make sure you start by going to System Preferences > Energy Saver > Computer Sleep and set it to NEVER. (You can leave the Display Sleep active). Make sure to follow Apple's directions for both making sure iCloud is ready to go, and for how to upgrade iPhoto. Before you start the process make sure NO other programs are running (they will either CRAWL or CRASH and will slow down your uploading process). I suggest not even opening another window in your browser except for the iCloud link. I am now letting them run when I'm asleep or will be away from the computer for extended periods of time.
It's a slow, slow process. The more photos / movies you have, the longer this process is going to take. Take a few notes on what seems to be completed and what isn't completed in both iCloud and Photos, and what editing features work and which ones do not in Photos. The reason I figured this out was that I wrote myself a few notes on what was working and not working, and then compared the notes with what I saw after letting the computer run for another 10-15 hours. I also suggest quitting/logging out and restarting the computer every 24 hours. That also seemed to pick up the pace of what was happening.
As far as I can tell, there is no status bar or indicator that "things" are actually happening (except the upload count on iCloud mentioned above.). Because this process takes so long, there SHOULD be some kind of onscreen box that explains what the computer is doing with Photos / iCloud at that moment, what it's finished, what it has left to do, along with an estimated time remaining. Most of the time I did not see any, moment by moment, updating being completed. Only after letting the computer continuously run for hours, and comparing the current status with my notes, was I able to see that progress was actually being made. MY POINT: Just because it doesn't LOOK like anything is happening ... that assumption might not be correct.
My last guess is that if you have lots and lots of photos and videos (I have 28,000 photos and 8 videos totaling less than 4 minutes), it's going to take a long, long time for your process to complete itself. I'm now over 72 hours of online activity with what I've got to work with. If you have 100K photos and 1K videos, it could be WEEKS before your process gets completed.
Good luck to all!! Thank you for all your help.