What's the difference between iTunes & Apple Music?

So I'm late to the party here, and I'm having trouble deciding my next move re: iTunes & Apple Music.

I have been using iTunes to organise my musical life for years. I use it's playlist functions religiously to categorise music into various folders and sub folders and I use the data from my iTunes library to send to external software (rekordbox 5) for when I DJ.

The key here is I need this music downloaded in order to export it on to usb sticks and to manage my playlists with ease. I buy music from all around the internet - I download MP3s and collate them in my library.

Another key is I LIKE to buy music - I often audition stuff on Spotify for listening at home and tracks that I enjoy I go to the iTunes Library and purchase to add to my 'collection'. I like supporting the artists more substantially by purchasing and track and I like owning the MP3's and being able to say, they're MINE (haha).

I began a free trial of Apple Music on my phone the other day as I am aware it's very similar to Spotify. I thought the idea of centralising my music onto one app would make things even more convenient than my currently library. But it seems totally set up for streaming and borrowing music in stead of buying.

`My computer asked if I wanted to merge my library just now and I am putting this off until I can understand how the whole thing works a whooooooooole lot better, because at the moment I feel like the process might be really stupid and difficult to undo.

Can you enlighten me as to how music purchases & downloads are handled on Apple Music?

Will Apple music still sync seamlessly and automatically with Rekordbox, or should I start looking for a 3rd party program to sync and organise all my music?

Any other suggestions are really welcome as I'm very nervous to start messing with my library.

Thanks in Advance