I actually stuck some eBooks on my PSP when I went out on holidays last time - they work pretty well, since the files are small, plus reading it doesn't use much battery.  I guess you could question about bringing books instead, but the PSP's somewhat smaller (and you can read it in the dark, if the place you're staying at doesn't have a bedside light).
So for homebrew, I'd say Bookr if you don't mind reading.

Can't recommend any homebrew games - they're great, but unfortunately, I wouldn't really play them for hours on end...

Plugins... personally use brightness control + vshex mod (CPU speed changer), but I think another plugin may include the 5th darkness screen level for the PSP, and most people are content with the XMB's CPU speed control.

Can't recommend for the other 3...