Hello Nikunj,
This error is caused when certain file types are not permitted to be uploaded on the server. You can learn more about this error here: https://tribulant.com/blog/wordpress/how-to-fix-sorry-this-file-type-is-not-permitted-for-security-reasons/
And as mentioned in the article, you can resolve this by adding the following line in your wp-config.php file:
define(‘ALLOW_UNFILTERED_UPLOADS’, true);
As for the selling feature, you can redirect all “BOOK NOW” buttons to your desired page instead of the cart page. You can do this by going to Appearance >> Customize >> Woocommerce >> Book Now Button Settings and providing the URL of the page where you want to redirect users.
As the theme is based on WooCommerce to create the products, destination and categories, you can not remove the woocommerce plugin itself for a proper working of the theme.
Thank you