Posted The Ultimate MP3 Audiobook Player Guide. This expands on these basic MP3 Audiobook Player requirements, and alters 3 and 4 - understanding that these make the experience better, having a touch screen with some kind of "track click bar" to jump between sections of the file with a single click can replace this feature. This involves the bar showing the current progress in the file and allowing a single click to jump to another spot in the file.
Rewinding and Fast Forwarding over boundaries is still a desirable feature in Audiobook Players (though potentially annoying in Music mode in some cases) - So being able to find an option to enable/disable this behaviour would be desirable.
PJPeter