I used to know how to do this whole predict thing manually but I haven't done this in months so please forgive me for asking. What is the log window telling me?

Actually the log window is more to help me to debug the tool if someone has a problem. And a log is also pretty to look .

More seriously, the log tells you the Q value currently tested, the average bitrate reached for each source with that Q, and then the "overall average" that is the "average of the averages". If this "overall" is equal to the bitrate targeted, then the prediction is concluded, else a new Q value is tested. I also stop the prediction when the diff between lowest and biggest Q value tested is less or equal to 0.01.