Hi,
plugin output can be customized by copying the appropriate template in your theme or child theme files.
All templates can be found in geodirectory/geodirectory-templates
In your case you need to customize geodir-author.php and add-listing.php
Adding variables to the author page should be easy, as long as the emember plugin provide functions to display them.
The add listing part I think is a bit more complicated.
I’ll flag this for the developers so that they can confirm.
Thanks for testing GD!