Select someone who can establish credibility with the team. People implement better when they believe. If the team doesn't believe in the facilitator then they may not believe in the plan. Be sure to select someone who has good chemistry with the CEO and the team. Select someone who can educate the team as well as facilitate the process.
All management teams have uneven experience.
This retreat is an excellent opportunity to learn. Select someone who can earn the CEO's respect. Select someone with presence. Executives and CEOs are a rowdy bunch. You need someone who can get the group back on course when they start of wander off.