1. Unclipped power means power at or below what your amplifier can deliver. If you could see what sound looks like, an unclipped signal would look smooth, while a clipped signal would be chopped off at the top of the sine wave, with a "Jigsaw" look to it. This tends to destroy drivers, especially tweeters.
2. This tells you the -3 dB point between the woofer to midrange (180 Hz), and midrange to tweeter (4.8 Khz, or 4800 Hz). In other words, both drivers are -3 dB at the crossover point - leaving (in theory) a flat response.
The crossover will then "roll off" the signal above 180 Hz for the woofer, below 180 Hz and above 4.8 KHz for the midrange, and below 4.8KHz for the tweeter, at a rate of 6, 12, 18 ... etc... dB per octave.
Each 6 dB is called an order. In other words, a first order crossover is 6 dB per octave, second order is 12 dB per octave ... and so forth.
So ... Let's say the B&W uses a 2nd order crossover - the woofer will be "down" 15 dB @ 360 Hz (one octave above 180 Hz) - the 3 dB down and an additional 12 dB from the slope, at 540 Hz, it will be down 27 dB.
3. This shows the resistance as "nominal" (I think you saw nominal, not normal, though in reality, "normal" would have been as good a choice in words) ... or 8 ohms is typical, with 3.5 Ohms as the minimum across the frequency band of the speaker. Knowing this is helpful when choosing an amplifier.
