Personally I use classic Windows Media Player and sync the folder between my house and my car. (Yes, my car has a Windows PC in it.)
I rip CDs I own, if you buy on Amazon you often get "autorip" when you purchase. Amazon's MP3 store is fine, I used to buy on Microsoft's back when it existed.
It is not that exciting primarily because I have limited time to work on it!
I run a copy of my home automation software (don't get excited, it's written in Visual Basic .NET) on a NUC in my car. The user interface consists of a 16x2 LCD display attached on my dashboard which displays the GPS position and speed of the car (I log this) as well as the song and artist when the playing music track changes, and an Elgato Stream Deck which sits in the center console and allows me the ability to launch playlists, advance tracks, etc. If it has Internet (it doesn't usually, I'm cheap), it can hypothetically do some limited navigation, but I haven't tuned the behavior of that much because it's hard (illegal) to program while driving.
I also really want to work on CANBUS connectivity, but it's a big project and I have bills to pay and kids to feed.
I rip CDs I own, if you buy on Amazon you often get "autorip" when you purchase. Amazon's MP3 store is fine, I used to buy on Microsoft's back when it existed.