You will need a Lifetime license for that since your users will be able to use them indefinitely.
But otherwise, it is allowed to use in this kind of product.
Hi, I have a page/site builder script. And i intent to use your website templates and themes in the script. My users will be able to customize and create paid and free web pages to my subdomain or their own domains using these templates. I understand that your $349 license is suitable for this use case?