A few questions about WP Discourse

Yes, just don’t give them access to the WordPress login form. You should setup a way to give your site’s admins access to it, so that they don’t get locked out of WordPress if your forum it down, or SSO is misconfigured. You can add the Discourse login link to any WordPress page with the [discourse_sso_client] shortcode, or by creating a link with this form. Set the link’s href to the Home URL of your WordPress site, set the redirect_to value to the WordPress page you want users to end up on. You can also add a link like this to your Discourse forum.

<a href="http://example.com/?discourse_sso=1&redirect_to=http://example.com/welcome">Log in with Discourse</a>

Yes, this should work if you are using WordPress as the SSO provider for Discourse. I’ve tested it quite a bit with wordpress.com as the authenticator for the WordPress site.

Yes, this can be done. It’s not a part of the plugin, because the idea behind the plugin is to improve commenting on WordPress pages. Discourse is designed to do this. Embedding a comment form would defeat that purpose for most cases.

The Discourse post_id and topic_id are saved as metadata on posts that are published to Discourse. You can use these values to publish to Discourse through the API.