Limit by num. of products selled

Hi guys,
thank you for your usefull plugin!
I can’t find anywhere a solution for this:
I sell handmade products and i need to put a limit for number of products purchased and not for the number of orders.
Furthermore, i don’t want to close the cart over the limit setted but i want to show a message to customers (on the checkout) over that limit that shows a delivery date (global date).

So they can continue to buy but they will have a communication after my purchases limit to show a new delivery date.

I hope i’ve been clear about my problem.. there’s a way to do this?

Thank you in advance!