It is recommended to run import on a fresh WordPress installation. For this you can use WordPress Database Reset plugin https://wordpress.org/plugins/wordpress-database-reset/ The plugin can be used to remove all the existing content and install a new version from scratch.
Please do the reset and reply with temporary wp-admin access, via the Private Content area. We will help you with the import https://xstore.8theme.com/elementor/demos/niche-market/
About the error in Theme Options, contact your hosting provider and ask to increase the SubstituteMaxLineLength to 10M or 20M.
One standard license is valid only for 1 project. Running multiple projects on a single license is a copyright violation.