Nowhere in anything you just said did you mention anything about talking to customers. I presume that's what the 3 co-founders will be doing, while the 3 engineers are building this "v1," but that a point I'd want clarified if I were in your shoes. If they aren't committed to getting out and getting in front of the customers (of if they haven't already done so, which seems to be the case) I'd be very worried.