I am trying to extend the plugin but I have some several questions that I think you guys might help me.

1. I am using the user plugin, how can I connect the user that registered there to be automatically in delegated authors?

Thanks in advance!

This is a bit more to explain than should be done here and also outside the scope of the plugin.
I can tell you that the relationships for this plugin are:

• RainLab\User\Models\User->hasMany( RainLab\Blog\Models\Post )
• RainLab\User\Models\User->belongsTo( FireUnion\BlogFront\Models\Author )
• FireUnion\BlogFront\Models\Author->belongsTo( RainLab\User\Models\User )
• FireUnion\BlogFront\Models\Author->belongsTo( Backend\Models\User )

You will have to assign those relationships at some point when they register if you want to do it automagically. If you understand the relationships then you can probably code this up yourself. If not then maybe someone can help you do it. But as I said above this is really outside the scope of the plugin and so I will not be able to help more.