Two iPhones, one computer, one music collection (This is not the usual "I want to share one Apple ID across two iPhones" question. Sharing an Apple ID may be the answer, but it's not the goal. I know of at least one other possible answer.)

Problem statement

How can I share about 10GB of music on a computer (most of it not purchased from Apple), along with its associated metadata, between two iPhones?

Current situation

I have a 20GB music collection. I ripped most of it from our CD collection. I got most of the rest from Amazon, Google Play Music, or sites with songs under Creative Commons licenses (free and legal to download). I purchased a couple of dozen songs from iTunes Plus (no DRM); if I need to, I can easily convert them to MP3 files that have nothing to do with Apple.

Currently, all 20GB lives on a desktop computer running iTunes. All the music is synced to an iPod Classic.  About 10GB is synced to my spouse's iPhone. The metadata -- playlists, song ratings, playcounts, etc. -- is shared between the computer, the iPod, and the iPhone. All three use the same Apple ID.

I like the PC/Mac iTunes application. I love being able to simply plug in my iPod or my spouse's iPhone and keep everything in sync.

I'd love that same simplicity with the new iPhone I'm about to get. I'm not sure what that implies for the choice of Apple ID(s) I'd use with my new iPhone.

Possible solutions

The simplest solution is to sync my new iPhone to the same desktop computer. Would that mean my iPhone would need to use the same Apple ID as my spouse's? How much of a problem would that be?

Another simple solution: I could clone my iTunes library (with a new Apple ID) and use it for my new iPhone. The metadata would start the same but fall out of sync; that's unfortunate, but it avoids any problems from sharing an Apple ID between two iPhones. I'd also have to add any new music to both iTunes libraries

Observations


Family Sharing doesn't help because I want to share music not purchased from Apple.
I don't need to share app purchases.
Most of our data (e-mail, calendars, contacts, photos) is associated with our respective Google accounts.
This article describes how to have one Apple ID for "iTunes &amp; App Store," and different Apple IDs for iCloud, Messages, and FaceTime. The article is about sharing an ID to share purchases, which is not what I want.


FYI, This "Think Different" question goes into even more detail about having different Apple IDs on one iPhone. Edit: so does this article on support.apple.com.

My spouse only uses iCloud for wireless iPhone backups. (I also manually back up her phone to the desktop computer using iTunes.) I expect my iCloud usage to be the same.
I already have most of my songs (but none of my metadata) uploaded to Google Play Music. Please see "I'd love that simplicity ..." above.


I'm afraid to start setting up my iPhone until I know what Apple ID I want to use. (I think I can begin setting up my new iPhone by choosing "Move Data from Android," then choosing "Skip This Step" when I'm asked to sign in with or create an Apple ID. Am I risking anything if start this way?)
The iPhones may use separate Apple IDs and share the same music library from itunes, (as you said, all of it is rights free / downloaded from Apple). The Apple ID only comes into play when syncing contacts, calendars, and alternate Apple Services. You shouldn't have any problems with Music syncing between iTunes and your new iPhone. Furthermore, you may download Google Play Music on your phone, and use the already synced content. The choice is yours. 

All the best!