1. Yes. It's a viable strategy to give someone half of the Lost Souls card then Bury it before they can rescue the second half effectively denying them the original point.
2. Depends what type you're playing. In T2, or T1 with Rescuer's Choice, you can use Burial on the soul your opponent chooses to attempt to rescue and that's an effective block since they can only rescue that soul.
3. No, Burial doesn't negate so any ongoing effect will last until the end of the current phase.
