You can find the screen at Mouser, where I bought mine. Note that they are out of stock of the white one, and 867 will arrive in 18 weeks, at time of writing. An identical part but with yellow rather than white pixels is available right now. These are all linked out of the Octopart BOM in the main thread.
Broadly:
- io is on a pair of stereo minijacks, rather than four quarter-inch/6.35mm jacks.
- there is no dedicated headphone output or headphone driver/amp. You can use most headphones from the L/R output just fine.
- power is supplied via a standard Raspberry Pi PSU. There is no battery.
The main thread, as linked to by @AlessandroBonino, is a good port of call for answers to these and similar questions.