Okay, so overall:
1) That signed defective PCB is just that, no it doesn't come with all the other parts of the Pandora, I doubt ED would sell the case + LCD + battery and so on for so little, LCD alone probably costs more than that
2) Screen is impossible without some active converter and custom cabling, there's no way you will be able to go from an HDMI out to parallel RGB, it's totally different. And this has nothing to do with the touchscreen, the pixel data signal alone is 24 lines, plus there's a bunch of other control stuff, backlight, speakers, power, etc.
3) I don't think RPi puts analog audio out on a header so your best bet is to hack something on the leads of the headphone port I guess. But AFAIK RPi's analog audio is generated by PWMs and is of pretty poor quality
4) I think you have the wrong idea of how the buttons and especially nubs work, there's no mechanical part you can separate from the PCB. The button membranes contact the PCB to triggera switch. The nubs are outright soldered to the PCB, and even if you removed them they're useless without the controllers that are on the PCB.
5) You can't power RPi with 3.7V, so the Pandora's battery is also useless
6) Pandora's SD and wifi/BT obviously don't work without the PCB and you'd have no way to access them anyway even with the PCB
Basically anything you want besides just putting it inside an empty Pandora shell won't work..
