Any integrated shopping carts that will do this?

Hi there,
I’m looking for a shopping cart plugin that will allow a special kind of product customization:

Here’s the deal-
This business sells custom sportswear. Custom in that the customer can create their own designs on a pdf template that they download (they do not need to pay for the template). But once they decide they want to order, they pay a deposit, then go through a series of steps in order complete the order, including uploading their design, getting approval, etc. They would also have the option of paying to have the item custom designed FOR them by someone at the company.

There should also be tiered quantity pricing. But the quantities should be on the total number of items, not the individual numbers of products. In other words, if they order 5 size small jerseys, 10 size medium, 10 large, the total quantity price would be calculated at 25 items.

I would like this system to easily integrate with WordPress, but if I need a whole separate shopping cart system for this, I will go that way.

Suggestions?

Thanks in advance.