No, users cannot delete their own posts after they have been submitted. We also do not remove posts per user request. Posts are only removed by site admins if the content violates our posting guidelines. Please carefully consider what you post in order to avoid 'post regret.'
No you can't. However, you can disavow them. That will mean they will no longer be linked to you and you will get no more notifications from them. Remember once you disavow them you can't get them back.
No, there's no way of deleting your questions. You can disavow them which is basically making them anonymous and disconnecting them from your account so you get no notifications or xper from them but that's about it :/