A suggestion or observation.

I think it would be better to display, optionally, the number of product on hand at the product detail page rather than at the view cart page. At the point of decision the customer should know if the product is in stock. Currently the customer doesn't learn this until the cart page. It's a negative customer experience. They've decided to purchase, added to the product to their cart, but then learn that it's not in stock.

Additionally, if you choose not to display product on hand the first time the customer is notified that the item is not in stock is a somewhat clumsy "Quantity of [sku #] On Hand is 0" message when trying to check out.

My 2 bits worth this morning,