Selecting compatible Raspberry Pi components

[Richard Owlett <rowlett@cloud85.net>]

I've been thinking about what a handheld computer COULD be.
My image is heavily influenced by my recollection of Palm Pilot.

My project goals are two-fold
  1. create a personal data logger reminiscent of a Palm Pilot
  2. become familiar with Raspberry Pi while using Debian as the OS

My needs include:
 >2 hours battery life
 4" by 7" nominal form factor
 touch screen input using a stylus
 display will be entirely character mode (40 chars/line would be OK)
 OS GUI not required except to say where stylus is
 OS shall be Debian {possibly with non-free drivers}

I've not found found user friendly selection guides.
A typical problem was not being able to know if a selection of 
components had mutually compatible I/O (electrical and physical).

Suggestions for suitable selection guides?
TIA