Reminded me of lob[1] and I think their colors / branding is too similar to your own which could be something to consider at this early stage.

How does the pricing compare to traditional printers? I think a better pricing user experience could go a long way to converting users into customers. Something like choose the product and a slider for quantity that shows the cost, discount and comparison to competitors would be a huge improvement. Tables also have their place so they should be accessible.

When's the API going to go public? I'd be interested to see how it's designed.