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I would suggest reading the Signal Analysis FAQ that's linked to near the top of your report. It does an outstanding job of explaining the concepts involved.
Now, to your questions in detail:
1) Why the Winegard antenna instead of the multidirectonal 8-bay?
Three reasons: First, you don't need a "multidrectional" antenna. See how all your channels are grouped together? The Winegard's performance will be perfectly adequate. Second, the specifications for your 8-bay were sloppily written. It is a UHF channel design, but UHF is 14-69, not 2-69. You will have a channel 10 and a channel 12, and those are outside of the design range for the 8-bay. Third, the signals are predicted to be strong to very strong in your area. You do not need a high-gain antenna for adequate performance of your system.
2) How can a pre-amp be overkill?
A pre-amp does not "clean" a signal, just raises the level of all signals and noise that enter it. As with any electronic device, the pre-amp will add a little noise to the signals that pass through it, so in reality the ratio of signal to noise and interference is actually a little worse with a pre-amp than without it. Pre-amps are used to overcome losses in the cables and splitters.
Yes, signals can be too strong for a preamp or tv tuner. Excessively strong signals overload the initial stage of either device, causing the strong signal to appear all over the spectrum in the device, knocking out reception of other channels. You may have encountered this behavior with inexpensive FM radios in the past.
Instead of buying a pre-amp, you may be better off buying a distribution amplifier, like the CM-3414.
3) Classic cable
We are telling you that classic cable should never end up being radiated by a home antenna. Cable is a closed system, meaning the signals stay in the cables between the cable company's head end and your TV set. Since the signals are never "in the air" cable companies can use frequencies not otherwise reserved for TV broadcasting. As GroundUrMast said, some of the frequencies used by cable are the same as used by aircraft and public safety agencies.
If you try to connect both your antenna and the cable TV feeds together with a splitter, the cable's signals will route both to the TV and to the antenna, which will then radiate those signals - a very bad thing.
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