This is both an amazing responsibility for you and a heavy responsibility. You will have the opportunity -- perhaps for the only time in your working life -- to not only have complete control over the technical solution, but if you are pro-active you may also have a say in the building the product, coming up with ideas for features.

On the downside, you won't have access to any senior technical personnel in the company to guide you or get you out of hot water. To mitigate this you will need to invest heavily in your continued technical education, which could mean buying learning materials or subscriptions to online courses and tutorials; at least, it means taking the time to do things right, to research thoroughly any new techniques or technologies you think the company needs.

While always striving to improve and to listen to your customers, you also need to have confidence in yourself and your technical decisions. It doesn't mean that you can't (or won't need to) compromise but it does mean projecting a professional image of yourself to your colleagues and customers. Obviously, the more you learn and the more experience you acquire, the more confidence you can bring to the role.

At the end of the day, like with any job, you should be willing to pack up and walk away if the situation becomes intolerable (as long as you leave things in a professional state).

But don't forget -- you are in the position right now that most programmers dream of. We started off wanting to just write programmes and build products for people who had the confidence in us to just let us do our thing; but then we found ourselves pidgeon-holed into roles predefined for us by IT departments. A complete programmer is like a complete painter, he should have a say in the product at all stages of its development. That means having the freedom to not just cut code or write tests, but to influence the design, to dream up new features, to have discussions about the marketing.

To an extent this role is YOURS to define. Have the courage to define it and to enjoy defining it. It might be the last time in your career that you get to do that, if you ever move on.