Sure, you can actually feature ALL your product categories if you want to.

Under the "Market Theme" menu tab in the administration area, click on "Category Images". On that page you can choose which categories are featured on the homepage.

Right now, we're implementing some improvements to the inventory control functionality with Paypal, and adding a "Special Instructions" ability to each product details page.

After that phase is done, then we'll be in a position to move onto discount codes/coupons.

It's probably not going to be for a couple of months though. But unless something critically important comes up that takes priority, it's next on the development queue.