You can transfer your music onto the BB1 (up to the limit of the capacity of the specific unit you buy). But the playlists will have to be built on the BB1.
When you are getting ready to transfer your music, it must be arranged with a folder structure like this: a folder for each Artist; each Artist folder contains folders for each Album by that artist; then each of those Album folders contains its respective tracks. Artist\Album\tracks
You can transfer the files in any of three different ways:
1) transfer by copying to a USB stick
2) upload using the WebUI
3) setup the BB1 as a NAS (Network Attached Storage) drive and copy direcly from the computer to the BB1
Once you have your BB1 and are ready, you can check back here for more specific instructions.
Back when I was getting ready to buy my first Brennan unit, I spent time reading the Brennan website. There is a lot of helpful information there. Once you've exposed yourself to all that, we're here to help you iron out the wrinkles.