Managing project managers

If you are managing project managers, thats what the PMO does. I would think you would want to start with a list of things you are currently doing right now and add the things you would like to do. That would be the what part of your answer.

As far as who, it depends on the size of projects and the number you have. The larger the workload, the more people you would want in your PMO. Also, I would believe you would want to include members from other functions like HR, Business, Marketing, Sales and so on available on the panel to ensure projects are done in a way to maximize benefit.

Overall, it seems like you are delegating your own tasks to a team.

I recommend that you develop a vision for what you want your PMO to achieve. I would first use the PMI's Organizational Project Management Maturity Model (OPM3®)—Third Edition to assess the current maturity and build a roadmap to get to the next level in maturity.

I would also consider using the PMI's Project Manager Competency Development Framework—Second Edition, to help you assess the competencies of your team and thereby identify areas for growth. My own director developed a self-assessment tool based on the framework, and used it as input to our objectives setting. It was a very powerful tool, and the most concrete, profession-specific goals and reviews that I've ever had.