Hello,
Everything seems clear. Thanks for the detailed description.
I can provide such customization for GravitView plugin. Think the best way is via custom plugin. So you will have just copy it to live-site and activate. But will see, if hooks are not enough, and some templates are have to be edited, then could be better via child-theme.
Ok. Please let me know (via private chat here) if you are interested in my help. So we can discuss all details.
I'm Serhii, wp-developer from Ukraine.
Br