Well, I already have the fully tested product for sale, so I don't need testers any longer. But if you PM me, I'll send you a code for a one-time discount on the kits.
The number of LEDs the Power LED Shield can drive at once depends on which Puck modules you install. At best-case and with the right power supply, you should be able to drive 3 parallel strings of 8 LEDs per channel, for a total of 96 LEDs on a single shield. Now that's only in theory and has not been tested. However, I have seen many cases where a string of 6 LEDs can be driven by a BuckPuck, using a 24 volt power supply. So if you did three parallel strings of 6 LEDs per channel, you would have 72 LEDs per shield.
These would have to be 1W LEDs (for a total of 72W) and you would need 1000mA BuckPucks in all 4 channels. If you had higher wattage LEDs, you could still get around 72-96 Watts total. It would just require a different connection pattern and the right power supply.
If you want to post your LED's specs, I can give you a schematic for the best possible utilization of the shield.