merging iCloud photo libraries
All my devices are on current operating systems as of this writing (1.12.18)
I just recently turned on iCloud Photo Library on my iPhone, iPad & MacBook- these 3 devices now share a common iCloud Library of 9,000 photos. Today, I've just converted my iMac's iPhoto library to Photos on my iMac (that's 40,000 photos!)- but NOT using iCloud Photo Library yet.
I've decided that I don't want my small devices to deal with a relationship to a library of 50,000 photos, so my plan is: [1] Turn OFF iCloud Photo Library on my iPhone, iPad & MacBook; [2] turn ON iCloud Photo Library on my 40,000-picture iMac. I will be satisfied to have iCloud-shared albums be the only photos I can access on my iPhone, iPad & MacBook.
Now my questions:
1) HOW can I get the current 9,000-photo library added into the 40,000-photo library.
2) if I leave My Photo Stream turned ON on all devices (including iMac), will my recently-taken photos from my phone appear on the iMac's library as I would expect it should?
iMac, macOS High Sierra (10.13.2), and iOS 11.2