Another question is.. what happens if a server spills a drink on it? :)
Now for an answer instead of another question. For marketing I would focus on finding a scalable sales method that is as self-serve as possible (small biz owners will always want to talk no matter how hard you try though). It's easy and tempting to go 'door to door' and sell one at a time, but economically it doesn't make sense. That's one place iOS helps, distribution through the app store. But you'll eventually need to find people who are generally looking for POS, not just specifically an iPad POS.
Anyways, good luck it looks interesting!