Now onto trying to find something to save all of my Apple music. Since I do not EVER plan on getting a subscription to Apple Music just to play what I ALREADY paid for!
I haven't seen anything which suggests that the new Music app won't be able to play your already purchased/downloaded music just like iTunes did.
I mean, you can do that on iOS devices already (with music that you have actually downloaded and synched to said devices), so I see no reason to think that you wouldn't be able to do this on macOS as well.