In my experience advising start-ups, you can never get enough hand's on time with customers, or potential customers. As Steve Blank says, get out of the building. Too many time opportunities are missed because the founder waited until he/she felt everything was "perfect". Your level of perfection can only be truly judged by the customer.
One of the advantages of doing beta testing is that your users will understand that the product/app may not be flawless and certainly will not contain every feature that they would ultimately want. So put it out there and engage your users in meaningful conversations about their experience. Listen hard to try and understand two main things: if the user doesn't like something, why? If they do, why? It's just as important to understand the reasons for your success as it is your failures, because at the end of the day, you win or you learn.
Good luck, and feel free to contact me as you learn. I may not know your domain, but I know about listening to customers.