Hi,
The order should normally be the same as what you have in the cart actually. So it's simply displayed in the order the customer added them, which is quite logical for them I suppose.
I suppose that if we wanted to add an option, it would actually be an option to control the order of the products in the cart (which would then snowballs to the order, the invoice and the notification emails).
Also, you're talking about ordering the products by "model" but there is no "model" in HikaShop. Are you talking about "brands" ?