Added: The example values for resistor values were just examples. There must be a theory that says whether it’s better to use bigger or smaller starting values (meg-ohm vs tens of ohms) but I don’t know the answer, so that would be worthwhile looking more at from an electronics perspective (come back and tell us the answer when you find it :))
As for monitoring the voltage, depending on the battery chemistry and discharge profile, and the power you’re using with your project, will vary how often you need to poll the battery. I would think that at your “full” state, you probably only need to check every minute. As the battery voltage gets to 7 you might want to check say every 30 secs, and as it gets lower you will want to check more often too, and ramp up the alerting to the end user (green flashing LED when all is well, slow red flashing LED when at your first threshold, rapidly flashing when it gets real bad, flash red/green when you think the brick wall is about to be hit etc). Obviously you don’t want to make things worse in your monitoring so you have to set some kind of realistic level that you’d never check more often than a specific time or flash LEDs to use more power than the rest of the circuit etc.