You can eliminate a big uncertainty by hiring people who have worked well together in the past, so long as they meet the required professional criteria. I didn't know any of the other New Focus people previously, whereas Iris Medical founders all knew each other well. Look out for wrong job definitions. One common mistake is to get a top salesman to be your vice president of marketing. He may not be good at managing, and sales is very different from marketing.
Small companies have little of the infrastructure support that exists in big companies.
You may not offer the environment that allows that person to succeed. Furthermore, that person may not have the experience to know there's a cheaper way of getting the job done. That sounds fair enough in the beginning because the roles you and your cofounder play seem equally important. Ownership should be based on future roles. The issue of ownership hits the pocketbook, but it's easier to address up front when the stakes are smaller.