1) GF will save the Form entry ID in the wp_usermeta table for the registered user, so you can grab all the entry(submitted) data and I believe the resume ID too
$entry = get_user_meta( get_current_user_id(), 'entry_id', true );
Then you can get the entry data using the “get_entry” method from the PHP API wrapper class as described in the docs:
https://www.gravityhelp.com/documentation/article/web-api/#php-wrapper
See: https://github.com/rocketgenius/webapiclient/blob/master/includes/class-gf-web-api-wrapper.php#L230
Or:
https://www.gravityhelp.com/documentation/article/api-functions/#get_entry
Also, you can hook to the GF post created or user activated actions and store the POST ID for that user in the wp_usermeta table, not sure but I believe the post created addon may have a hook for that.
2) See: https://wordpress.stackexchange.com/a/5048/60079
3) You can add a hidden field to the form, save it as user meta and update the value if they complete the resume using the “gform_post_submission” GF hook.
I don’t like the idea of forcing users to complete the resume, instead, I’ll go for a site wide notification. Anyway, you can hook the wp init and always redirect the user to the desired page and hide the navigation on that one too.