Yeah, enemy movement sound effects are probably a good idea.
You can currently jump higher by changing the gravity with a script, but you'll fall down slower too, so I'll consider adding player jump height.
And no, I'm not aware of a bug that duplicates entities when loading saves.
1.8 fixed a bug that would cause doors to duplicate when loading, which might have been caused by the same issue.
But if you're still experiencing a duplication issue in the latest CE version, I'd love to discuss it with you so we can find the cause.