1. Not sure but I don't think so. The subscription feature allows access but not per post
2. Yes users are assigned to groups and each group can be set to allow or not for searches.
3. Little convoluted but yes. You can set permissions to forums where a group is moderated. After x number of posts they can be promoted to another group and then you can say they are not moderated if you choose. And you can pick and choose what forums are or are not. So you have complete flexibility for this.
4. No, People can subscribe to posts to get email notification and you can select to sent a post via email to a third party. But there is not a import from a email to a post.
