Recommended crossover is 2khz or higher at a minimum of 12dB/octave slope for high power use. If using with lower power you can cross it much lower
20 watt RMS, same as about any other compression driver with a 1.3" coil. Don't fall for the supposed high power hype of others, especially in the "car audio" world ;-) A tweeter will see very little power if crossed over properly and these guys can get extremely loud