Why now? Family Plan seems to allow tracking multiple devices with [FindMy](What is Family Sharing? - Apple Support), We both temporarily lost our iPhones at a different time in the last month which was the wake up to make me consider this. And we’re going overseas in a month.
Current status:
We use a shared AppleID for purchases. Music and Apps. I did this (ten?) years ago and IIRC that was the only way to do share purchases. That ID is linked to a personal domain email.
Both have AppleIDs and each have several devices (iPhone, MBP, iMac). My ID is a me.com email, but my email is mainly on personal domain. Her ID uses her email on our personal domain.
We have an AppleTV and two HomePods. AppleTV uses shared ID. HomePods respond to both of us (more or less).
Although we can share apps this way (most allow a few users anyway), we probably don’t really use each others apps enough to matter. In other words if app sharing depends on that common ID we could give it up. 1Password is a family subscription, so I assume it doesn’t depend on this shared ID. The two other subscriptions are not used by my wife.
But we do share music. We buy some music, but we have a pretty eclectic collection and much of it from DVDs which we access using iTunes Match. We listen on the HomePods and iPhones in the car.
She uses Photos, but downloads iPhone photos manually to Albums. My iPhone photos are downloaded to my computer via Mylio. I also download photos manually on my computer to Mylio. So I don’t care about what happens to my Photos’ photos
I use iCloud 200GB account that I’ve been using for my Documents folder.
Plan to add some AirTags to the mix.
What will the downsides or gotchas of adding a Family Plan? A challenge may be to move our current shared iCloud account purchases to one of our iCloud accounts.
(I now also see Apple One, but that’s essentially a package of services which at present doesn’t impact us. We’re only using iCloud+. Might use Music in the future. Apple TV+ maybe. I only put this in here since it’s part of the Apple service possibilities and it’s hard to keep track of all of them.)