A single order can hold as many items as you need, and this is how most orders work. You are not limited to one seller or one product.
On your quote, each item is priced as its own line, so you can see what each costs. The handling fee is calculated once, on the combined subtotal of all the items, not added per item. What the handling fee covers explains it.
We purchase your items individually, often from different sellers, at different times and prices, and receive, inspect and photograph each one as it arrives. Your order only moves to purchased once every item has been bought, and to inspected once every item has been received and inspected, so its status always shows the whole order.
Shipping is quoted once, on the combined weight of all your items. How shipping is quoted explains it.