i will be following this thread closely - i am not quite as far along as you are but am working to put a trailer together. I can contribute some info about payments - there are a few companies that offer a service that works with iPads and iPhones -
https://www.iphonemerchants.com/ - if you want to accept plastic - I think the payment costs 2.5% of the transaction and the two people around here using this kind of system just tack it on to the bill - personally, i don't mind paying it as it is easier than hunting up a cash machine.
Cheers!