I wouldn't worry so much about WhatsApp suing you. If they don't like what you're doing (or others for that matter) they can more just change their protocol.

The problem with building a company around such a solution rather is this: Is there a market? Sure, having a machine automatically answer customer requests is a nice parlour trick but what's the benefit for the customer?

Just saving money on call centre agents? Or does the software actually solve a real problem in a novel way that can't be tackled using existing solutions?