Yes, WooCommerce is integrated and fully functional in SaasLand. You can build your own store using SaasLand.
Yes, SaasLand is compatible with Gutenberg.
Yes, SaasLand is compatible with WordPress 5.0 and higher versions.
SaasLand comes with “Elementor” which is a very advanced, drag-n-drop page builder. For Elementor related issues, you may check their support: https://elementor.com/support/
The payment is one-time. After you pay the one-time price of the theme, you will never be charged for it. But you can buy extended support after your support expires after 6 months.