Q: Can Cart2Quote automatically check the inventory level before allow customers to add cart to quote?
A: Cart2Quote follows the behavior of Magento. So if you set in Magento that an out of stock product can still be ordered, than Cart2Quote will also allow this product to be quoted and be converted to an order.
To allow quote requests for non orderable (out of stock) items would be complicated as when a quote with non orderable items is accepted and converted to the checkout - Magento will inevitably generate an error as Magento cannot process the order.