Product Quantity and Varity Numbers Differ

[UndoubtedlyMad]

I am offering made to order sweatshirts in sizes S-3X

I have 45 sweatshirts in stock in those various sizes but only want to offer 15 avaible so that I am not flooded with orders. How can I do this?

The other issue I am running into is I want to add the option to add matching earrings to their order for an additional fee but I do not see any way of doing this. 

Thank you in advance for the help!