User registration is being processed through the default WordPress registration system. So you'll need to find it in Wordpress settings. 

Are they sent an authentication email once registering before they are able to comment?
I ask to avoid having spammers post without needed to authenticate a valid email address.

No, wpDiscuz doesn't have it's own registration/login functions. It's the Wordpress functions.

However, this can be reached because the user in Wordpress and wpForo is the same.

I mean if you disable guest commenting in wpDiscuz the users must be logged in to comment that is the user already exists in Wordpress (this is the same in wpForo as well).

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wpDiscuz is a free plugin, so you can install and test it. It's a native comments system, all comments are stored in WordPress tables, so you can install and uninstall the plugin whenever you like. Information will not be lost. 

So wpDiscuz has a register/login function that will add the person as a subscriber (or other Wordpress user type) in my wordpress site?

Meaning if they register with wpDiscuz they can use the wpForo forum and vice-versa?

In this case, you should disable comments for guests. More info here: https://wpdiscuz.com/docs/wpdiscuz-documentation/getting-started/custom-comment-form/comment-form-settings/#only-loggedin

If I integrate wpDiscuz on the site for our articles will logged in users from the forum be able to comment straight away?

yes, this will work fine. The plugin is free you can install and check. 

Are users that register to comment on wpDiscuz added as a 'user' to the wordpress data base?

Yes, the user data are stored in wp_user, wp_usermeta. wpDiscuz doesn't have any user registering feature. 

Will it use their same gravatar image from the forum in wpDiscuz?

When the wpForo is enabled wpDiscuz will get avatars from the wpForo plugin.  

I also saw on another site that their articles are automatically added to the forum, how can this be automated to occur?

This is a wpForo add-on. It calls wpForo – Blog Cross Posting. You can check it here:

https://gvectors.com/product/wpforo-cross-posting/

wpDiscuz is a free Wordpress plugin. The demo version is here: https://wpdiscuz.com/demo/

Are users that register to comment on wpDiscuz added as a 'user' to the wordpress data base?
ie. so they can then use the forum and I capture their username and email? I want to make sure they are not entered in the user database twice...once for the forum and once for wpDiscuz.
Will it use their same gravatar image from the forum in wpDiscuz?

I also saw on another site that their articles are automatically added to the forum, how can this be automated to occur?

Willing to buy the full version of the plugin if needed, not a problem.