Hopefully someone will be able to chime in here with an answer to that question. I also started with iTunes and switched to Apple Music a while ago. I had no problem with my old iTunes songs being available in the Apple Music app, but did not have playlist in iTunes to see if they transferred over as well.
I really like the Apple Music service and have added HomePods to further take advantage of it. I can play any song I want whether I'm at home using the amazing sound of the HomePods, in my car, or anywhere else listening on AirPods from my phone. I think you will find your Playlists will change more frequently, since it is so easy to tell Siri to add a song that is playing to any playlist that your want.
Apple Music does a pretty good job of creating a personalize radio station for you depending on the initial Genres and Artist you choose when first set up, as well as songs you have in your library and furthers customization when you tell Siri if you Like or Don't Like a song that is playing.