Choose a developer who focuses on Drupal, not just "PHP."
Many contract PHP developers say they know Drupal, but dig a little deeper and you'll discover expertise is hard to come by. Drupal is a popular, widely-used PHP framework but it takes time and effort to master. Just as I don't claim to be a Wordpress developer (though I can refer you to some awesome people who are!) not just any PHP dev can service your mission-critical Drupal site.
Ready for Drupal 8.
Brad is experienced in Drupal 8 and is a recognized subject-matter expert on D8. Selecting Drupal 8 is a great option for new-build projects and upgrades, but this later version represents a significant change in development practices. That means your web vendor must be personally invested in learning and staying up on the latest trends, not just content with the comfort of Drupal 7. Before hiring a Drupal developer, ask about their expeirence with Drupal 8.
Don't pay a developer to learn Drupal on your dime. Read "Questions to ask when hiring a Drupal developer" for tips regarding judging the experience of a potential web development partner. You'll see why experience and community engagement are central to picking the right developer for your project. (And why I'm happy to highlight my credentials in both these important areas.)