Minimum quantity by product category in Opencast

We need to set a minimum Quantity in an Opencart so orders can be processed. Main requirements are: 1. The Cart must meet the minimun quantity per MAIN CATEGORY in Opencart (does not apply to subcategories), before the customer can go to the CHECKOUT PAGE. 2. When the customer access to the cart page the error messages must appear inside the context of the page in the upper part. If the customer is not selecting the minimum quantity (PER MAIN CATEGORY). There must be an error message per every main category where the customer is not selecting the minimum assigned quantity. 3. The PROCCED TO CHECKOUT BUTTON must be disabled until the customer selects the Minimum quantity desired. 4. There must be a piece of code that REDIRECTS a customer to the cart Page (with error messages detailed in Requirement Number 2) If the customer tries to access to the checkout page without having added to the cart the minimum quantity established by category.