As tempted as you are to dive right in, you don't want to rush into things. If you are still working on your prototypes what will you have to sell or demonstrate? If you're pretty confident you will be ready with your prototype, you still need to allow sufficient time to develop an inventory.

How far along are you with the business end of the business? If you want to accept credit cards you need to be set up as a credit card merchant. To do that you need a business bank account. To get a business bank account you need to have your business registration or reseller ID or incorporation papers.

Having only business cards to hand out will make it obvious that you are new and not quite set up. You should have brochures or handouts and certainly you should have a website. Your customers will want to learn more about your business. Usually at a conference the attendees (potential customers) rush from booth to booth gathering info and will likely want to check you out further (website) before committing to any large orders.

Take a deep breath and slow down. Complete your start up tasks before you put your product out there prematurely.