What struck me the most is going with the old and tried tools (PHP+MySQL). Nowadays everyone - myself included - is trying to have an excuse to try the sexiest JS framework of the day and most of us fail miserably to deliver anything useful - because of lack of experience or just reinventing the wheel altogether. Old and boring is still sometimes the best.
One of the hardest things for programmers to learn (including myself) is that success is almost entirely determined by how well your solution solves the problem you're aiming at, and how well you market it. The tools you use to create your solution matter to almost nobody.
It's true that if the company really grows, scalability, code manageability for teams etc. might become an issue if your backend is very poorly engineered, but that's the exception to the rule. As long as it works, it's good enough to launch with.