Take the iCloud Plunge?
Solution 1:
- Back up your devices
- Jump in the iCloud pool
- See if you like it
Given your landscape, having one set of photos instead of managing them on many devices alone seems worth simplifying things via iCloud. I'm also a big fan of iTunes Match and Apple Music despite having tens of thousands of CD and phonograph recordings digitized.
Solution 2:
Another perspective, from someone who's had iCloud since it was .mac
We have 2 Macs, 2 iPhones & an iPad, shared across 2 IDs [myself & my partner]
We set up Family Sharing to cross-pollinate all our purchases, music, books, apps.
We share certain portions of our calendar with each other.
Contacts are not shared between IDs - that you would have to do manually.
Computers all use Time Machine plus Backblaze. iDevices are backed to iCloud every night, & to iTunes before any iOS update.
Photos are all kept locally, not in the cloud (I don't grok that bit either ;)
Music is all kept locally, no Match or Apple Music etc.
That also means no extra subscription charges for iCloud storage etc.
Been perfectly happy this way for years.
Benefits:-
Synced calendars to all devices [inc the shard parts to each separate ID]
Simple things like looking somewhere up on the map, then immediately having that data in the phone, on the go.
Bookmarks & passwords synced, so I don't have to remember them all.
It's all completely free, so long as you stay under your 5GB storage limit, which is easy without photos & music.
So, you can go halfway & still get some benefit.