Amazing story and outstanding save, well done! Your decision to take a good free diving course with the folks at FII is an excellent one. Your already good free diving skills should advance noticeably during the course. More importantly they will teach all about blackout, the outward signs that might show up in your buddy, symptoms in yourself, protocols to try to avoid it in the first place and physical recovery and reviving procedures for a blackout victim.
In bringing a blackout victim to the surface it is important to keep their mouth closed to try to avoid them inhaling water. This may well have happened before you even reached him at 20 ft. perhaps making it a moot point in this instance. It is a great thing you were paying attention and interceded successfully to save his life. FII teaches how to support the diver at the surface and coax him to breathe again if no water has been inhaled. You will practice these skills in the pool and in the ocean while evaluating the background during the discussions. I've seen six guys blackout in controlled circumstances in competitions and each one was breathing again in seconds using these techniques. No CPR was administered or needed in these cases, again if water is inhaled things become much more complicated with the outcome uncertain. Another procedure they will describe to you is one diver down, one diver up to act as safety during dives. There is still a lot more that they teach you in the Level II course. More info at:
http://www.freedivinginstructors.com/ The fact that you took CPR training and applied what you learned so effectively is another very good thing. The success rate in reviving someone with no pulse is fairly low. Great job in bringing him back and thanks for sharing your story. People could do with better awareness of blackout hazards and training to try to avoid it.