1. You can use User contributions and configure the web parts to use the blog post page types, set appropriate path in the content tree and so on. User contributions allow the users to contribute to your web site - in a form of wiki articles, blog posts or any other content. This content is stored in the content tree - in Pages application as any other content of the web site.
2. If you do not want to store these blogs in the content tree, then you need to create your custom module with all custom logic and do not use the Kentico's built-in blogs and user contributions modules.
3. By default no - unless you will create fully custom module with custom logic on your own.