I wish Jesse would respond. Last time we had something like this is took a couple of months to get his attention.
To answer some of the questions I would have to guess.
1. I have < 3000 Music tracks and 100s of those are a Bible Study so they don't get mixed in.
2. I refuse to use Apple Music
3. I still use Code Monkey's stuff too.
As for your questions:
- It looks like you can integrate Apple Music into your library.
- Once it is in your library, the Smart Play list method should work. My guess is that you would have to download the track for it to work properly. I think the Smart Playlists would only work for offline music.
- I don't see why the 25000 songs would affect anything. Unless you are using Match.
- I would expect that since iTunes Music compares tracks from your library that are in the cloud, the cloud based tracks will NOT have your tags. If you use the playlists, and listen to offline music, the tags would be safe. If you accidentally download the same track you already had, I would guess you would lose your tags.
- I expect that Apple will leave all of your music offline. Adding tracks you tell it to (maybe even recommended tracks) to your library. They have to handle the case where you discontinue the service. When you leave, all the offline tracks should be disabled. All your original tracks should remain. They had to have thought of this and would leave your library intact (possibly with encrypted inaccessible iTunes Music tracks mixed in, but you should be able to find them and remove them too) so you are able to get back to your music.
I have no experience, other than knowledge on Smart Playlists, and iTunes use.
There are plenty of posts of iTunes Music messing things up on the Apple Forums. Though how many of those are people that don't understand iTunes to begin with, is probably the biggest problem.
I personally think that spending $10/month to get more music, is not something I need to do. I don't care about recommendations from Apple, connections to the Artists, any of that stuff. Yep, maybe I'll spend more obtaining a few tracks a year, but I'll know they are tracks I want, and no one gets to bother me with recommendations. Besides I doubt I spend $120/year in music.
I think iTunes Music is going to become Cable TV. Cable started out as a place to get more channels without commercials. Since then the price increases, and ads have been inserted in. Try and get away from it and record shows you want. It is possible but difficult. What are artist contacts and Apple recommendations but ads for other music? What is it that Apple wants? Constant income. Millions paying $10-$15/month for decades. And when they leave the service, all that music they were listening to is gone, and will probably need to be re-purchased if they want to keep listening to it. They could get lucky and those tracks are not popular and drop the price a bit.