You need conviction in your own beliefs, and the willingness to ignore others naysaying.
No matter what you choose, build stuff and be around smart people.
If you can just learn to think about the market first, you will have a big leg up on most people starting startups.
In the early stage of a startup, hiring senior people is usually a mistake. You just want people that get stuff done.
A single mediocre hire in the first five will often in fact kill a startup.
Just put a little pin in your mind: when you cross 50 employees, there are a new set of HR rules that you have to comply with.