Based on what you said for #1, I assume you'd have to listen on the player move event and set a timer that is only cancelled by another move event?
If you're AFK, you're not sending movements events, I think this isn't a good option.
And one question, What if you're lagging, will you be killed then? (You 're not sending any package).
Ehh, I'm not a DEV, (But I know some things :D )