How long should the feedline be?
Roughly, it should be equivalent to the length of a slice of bacon, multiplied by as many as you consume in six months, and then again multiplied by the average of your front and rear tire tread depths as a decimal.
Which is better, RG-58 or RG-59? (trick question)
I always start any discussion about coaxial feed lines with the recommendation to solder the center conductor to the braid as close to the receiver or transmitter as possible. This almost always eliminates significant variation in coaxial feed line performance. Thus, I buy the cheapest coaxial cable I can find.
Will using oxygen free copper speaker wire for the radiating element allow me to hear WABC in the Mt Kisco A&P?
Using oxygen free copper wire introduces the risk of the bends; I never recommend it without proper decompression to stabilize the ambient pressure inside the insulation.
Is it true that wrapping 666 turns of the feedline around a stack of $20 bills will attenuate all Brother Stair transmissions?
This depends on the dollar currency in question; Canadian versus American dollars have a very high variation in capacitance which can significantly alter the attenuation properties of the filter you reference.