28 hours with light is very close to what I've
estimated and never had the discipline to test in practice - good to know.
Without the light you will get much longer - on a scale of weeks even with wireless turned on.
There are many dictionaries available for Kindle, including translation dictionaries. My friend's wife (for whom English is a second language) finds these extremely useful.
As far as book management goes... there isn't much to it. Kindle is optimized for "buy-read-end-to-end-close-and-never-read-again" scenario that works well enough for me.