There is nothing in uStore out-of-the-box that will do this.
I can give you some suggestions:
1) using "add javascript to storefront" you could add some javascript to check the total amount on the "order summary" page and if the amount is less than your minimum
a) disable the checkout button, and
b) display a dialog that tells the customer to add more items to the cart to reach the minimum order amount.
2) The shopping cart page is now in react JS, so you could probably apply the same logic on the checkout page using React JS.
3) Consider using a different ecommerce solution that provides this functionality, and add dynamic products to that system by using uStore Connect.
4) Submit a feature request to the uStore product manager via your support rep