don’t make this complicated. what kind of port does you car offer? is it a USB port?
if you have a USB port, my car has one, then you should be able to simply plug in a flash drive with mp3 files on it. That’s it - don’t need an ipod, mp3 player at all.
In my car, I have a simple common flash drive with maybe 700-1000 mp3 files on it divided into 4 folders based on type of music. Plugs in to the USB port and I listen to the music.