The short version:
(1) Will more club world seats become available for pre-selection prior to T-24 online check-in?
(2) If I pay to select seats now, will I be allowed to change my mind before the flight, or is it a one-time change? (What if I choose lower deck, can I then upgrade to upper for €12?)
(3) Is it common for all the "good" seats to end up taken prior to OLCI?

The longer version:

My wife & I will be traveling on BA0179 from LHR-JFK on Nov 7. We are newbies to Club World seat selection. Our preference is: upper deck if possible, and either row 12, 14, or 20 (we like the back row of the cabin) on lower. I am happy flying backwards, but she will not be. I would love to hear your suggestions for strategy to get our preferred seats on this flight!