Q2: For the basement gigs and small to midsize rooms, the 25x40 size your talking about, 900 watts total should be ok, but that's using both A+B outputs, but 900 watts won't cut it outdoors.

Q3: The question here is how low an impedance can you drive out of each output?

Q4: If you can't drive 2 ohm's out of the mixer your maybe asking for smoke out of output A. Output B would be fine because that's a 4 ohm load with 2 monitors. The second part of that question wouldn't work either because the mono output just ties A+B output together.

Q5: Nope not from a single cabinet. Folded horns it's all about throat area,horn length and especially mouth area.

Q6: You only need 1 active x-over for everything.

You didn't break any rules of the board, ask away that's why were here, to help out.

HTH
Bill W.