Battery life depends on how you are using it. I would estimate about three hours at worst. I typically use mine more than six hours daily and switch batteries at least once. I have my brightness at about miniimum but can't tell the difference.

There is no problem with reading pdf files of any length that I have encountered.

Independent software development is pretty active and seems to me to be accelerating.

You can get a pretty good idea of the answers to your questions by browsing the forums here, and the maemo.org pages.