My dap has an SD slot and can go up to 2 tb I think but currently has a 500gb in it. Copy over music to it on pc.
Only difference in use to a phone is it's WiFi and doesn't use a data chip. If you need a internet connection when out and no WiFi is around, you can make a hot spot with phones data, if your phone allows it.
I also changed cables on cans to 4.4mm balanced. Superior sound.