Aproximately, yes (~6million versus ~3million)
Not sure, but I can look up the cell diameter not including the walls. From that I can calculate the cell wall diameter from the cell pitch.
Even if it is the case the light output would still be lower. This is because the smaller your make a plasma cell the lower the efficiency due to smaller phosphor surface area and the smaller the discharge area. Also, the plasma discharge comes too close to the wall of the cell and loses energy to the wall (called wall loss).
However, Pioneer has redesigned the cell structure several times over the years to increase efficiency (I think they were the first to be able to produce 1080p at 50" size) such as deepening the cell to increase phosphor area, and using a vapor deposited MgO layer covered with a crystal deposited MgO layer (crystal emmissive layer) to increase discharge probability (and efficiency). With this they achieved 1.8 lumens/watt at 1080p resolution.
With the Kuro panels they have apparently used a secondary MgO (or diamond) layer at the bottom of the cell to increase efficiency and lower the need for priming (resulting in reduced background luminence-lower black level).
To make things even more complicated, the more pixels you have in a plasma the less time you have to address them (one line at a time). And since plasmas use a time-pulse-width modulation to generate grayscale , the brightness is also reduced because there is less time available to emit light.
Altogether, low brightness with 1080p plasmas was one of the biggest problems slowing the time to market but now that cell efficiency is up, and addressing speed is up, the brightness should not be an issue for the consumer.