As an entrepreneur and founder of a mobile app startup, what are skills that are required for me to know? Do I most know marketing? Do I most know programming in a specific language? What are the skills that are required and/or at least recommended to master for me to be successful?
The answer is what you do best!
I have seen from programmer to UIX Engineer to Marketing or someone who dont know any of this managing App Developing Team. As any other business knowing HR and having clear vision and understanding of the industry is most important. In generally a Mobile App StartUp should not be a very big Team, I am assuming 3-10 is ideal team size. But retaining good developer and designer in most demography is a challenge. If you have not a programmer you could hire a CTO, if you are not a marketer you could hire a CMO. But to really run a company like Pro, a insider you have to have clear idea, which language, framework platform you are using, how marketing for your specific sector. You dont have to code, but you need to have basic idea, so you could at least understand your team's work load and time frame. Or you could also have a co-founder who knows what you don't.
I hope it gives you some idea. I could give specific answer if I know your specific situation.
Best of luck!