Your comments
There should be a link under the plugin on the Plugin page in WordPress or you can go to the Account Page inside the Plugin and there should be a button to enter a license key.

Sure. That feature uses a third-party service here...
You should be able to add the background color to the image with the background parameter like so...
https://avatar.oxro.io/avatar.svg?name=Eddie&background=f39c12
For Template Style 1 look for the following file. (different depending on the template style)
\wp-review-slider-pro\public\partials\template_style_1.php
search the file for this...
https://avatar.oxro.io/avatar.svg?name=
There are two locations. And just add the background parameter to the URL.
I can add this to the list of requested updates. In the meantime, you could do it with a custom child theme. More info here...
There is a way to do it, but it will require a plugin update for me to add that feature. I can also tell you which file to edit if you would like to modify the plugin yourself. I'm probably about a week away from an update.
I'm not exactly sure what you are asking, but you can create a review submission form to collect reviews. You can include links to other review sites so they can go leave a review there if they want. However, the plugin can not submit a review to Google for the customer. Google or any of the other sites require the customer leave the review on their site.
I would need to log in to your site to investigate. You can send temp admin credentials to landjllc@gmail.com if you want me to take a look.
It checks the name and timestamp of the current reviews in the database and compares them with the import. If a duplicate is found it skips it. So, they add unless already in there. They do not overwrite.
Customer support service by UserEcho
Yes, you would need to delete those Google reviews that you downloaded with the Free version. They aren't going to have the owner response. Then you can re-download them with the Pro.
You could add a read more to the owner response but it would take some programming. Basically separate the response with PHP and add some HTML tags like <span> around them. You would hide/show the second half of the response. You would need to it with either some CSS.
https://stackoverflow.com/questions/6019845/show-hide-div-on-click-with-css
or some jquery/javascript...
https://www.w3schools.com/jquery/jquery_hide_show.asp