Yikes! Ask the tough ones. Ok, here goes:
1) For the purpose of the following questions, can it be assumed that the cloud-base and ground combination act like a large parallel plate capacitor? Not exactly. The charge separation mechanism in a supercell is much more complex than a capacitor. There are layers of charge inside a cumulonimbus cloud, and the whole system is highly dynamic. Trying to model it as a simple plate capacitor is overly simplistic.
2) If the cloud base is -charged and the ground is +charged, then presumably drops falling from the cloud will also have a -charge. If this is true, would they not be acclerated towards the ground at a speed somewhat greater than due to gravity alone? The ground is considered to be at 0 volts, and has neither a positive nor a negative charge. Raindrops don’t appear to have a strong charge either.
3) Similarly, if rain is falling, would it not act to blead off much of the cloud’s charge? Have there been any studies that correlate heavier rainfall with less lightning? There does appear to be less lighting when the rain is falling harder, however this has nothing to do with bleeding off charge. It is believed to be caused by a choking off of the strong updrafts which are thought to be important in the charge separation mechanism, the exact details of which are still largely unknown.
4) If a bird took off from the ground below a charged cloud, presumably it would have a +charge. As it flies higher into the sky, would it have the potential to induce a lightning strike? No, see #2 above.
5) What about aircraft? If they fly into the storm from elsewhere than presumably they would not have a net charge and as such would not “attract” lightning, correct? Do they just get hit due to random chance? Does the bolt pass through the aircraft and continue down to ground? Aircraft actually appear to induce lightning to strike them. Several studies have been done deliberately flying aircraft into strong storm cells and observing the results, the the planes get struck more often than mere chance should account for. The exact mechanism by which this happens is unclear, but it is believed to be the result of the same effect that causes contrails. The nucleation sites created by the passage of the aircraft lays down a path for lightining to follow, triggering a strike. And, yes, the bolt is conducted through the metal fuselage and out the bottom towards ground or another oppositely-charged cloud.
6) I was watching a tv show about lightning and they said that there is a particular radio frequency on which you can hear lightning from all over the world. They never said what this frequency is. I would guess that lightning would produce all sorts of crazy radio frequencies; is what they said true? Lightning produces RF noice across the EM spectrum from longwave radio waves to UV. Low band radio travels farther, all things being equal, so you are more likely to hear the pops and snaps caused by distant lightning on something like the 160-meter band. (around 2 MHz) than on normal broadcast AM. Even so, such sounds would be difficult to positively ID as lightning, since a number of phenomena can cause similar sounds.