Shipping Zones Different Product Minimums

Website is currently set up to sell coffee to the United States only with a flat rate shipping charge. 

Client would like to offer free shipping on orders over qty. 4 but also include Canada and Mexico. Only orders being delivered to the Untied States could be for less than qty.4. 

Wondering how to set this up? I know there can be coding to enable shipping minimums and I could change the shipping zones, but then how can I keep the ability for small orders with chargeable shipping to be able to be delivered in the US. 

Whilst you could technically code a solution for minimum order quantities you can't strictly enforce it. This is because the checkout page gives customers the ability to adjust the quantities that they have in their cart. You cannot change this or add code to stop people doing this on the checkout page, as the checkout is locked down in order to be PCI compliant.