You don't need to make the structure complicated, in fact you shouldn't. All you need is for every employee to know who their manager is.
Every thing at a startup gets modeled after the founders. Whatever the founders do becomes the culture.
The thing that kills startups at some level, is the founders giving up.
Growth solves (nearly) all problems
... how much time you should be spending on hiring? The answer is 0 or 25 percent.
It's difficult to get large groups of people, to the extreme levels of focus and productivity that you need, for a startup to be successful.