Is there a minimum quantity of products i can purchase?

Yes there is. Each product has a minimum quantity of packs that can be ordered, the minimum quantity is set by default. A box of the product contains the minimum quantity per pack.

So if an item has a minimum quantity of 40 (which is equivalent to a box of that item), a reseller can buy 40 packs, 80 packs, 120 packs. You can use the + and – buttons to increase or reduce the number of packs you want to order.