Hey @MZ welcome to the Seller Community! 

You can use Square to manage your inventory. We actually have two levels of inventory to choose from! We have Basic Inventory Management for tracking how much you have in stock. It will automatically deduct items from your inventory with each sale. You can also set up stock alerts. 

Inventory Plus is apart of our Square for Retail product.Inventory Plus will allow you to enter the costs of goods, projected profits, inventory by category. It also includes the features of Basic Inventory Management. 

At this time Square does not have an integration with Amazon.