Hi,
Sorry, I don't really understand the issue. You say:
So I understand from you that there is no way to make an option required in Hikashop.
But as Jérome said, it is possible thanks to:
When you configure your options products, you add a characteristic with all the values you want in the dropdown as choices. If you don't have a "no" value in it, you won't have a non selectable option.
So as said, this make the option required.
To have a discount on the product based on the quantity bought, you can add many prices on the product and set a minimum quantity for each prices, this way you will have discount based on the quantity.