Yes.
Not necessarily. Remember AM and FM radio waves go through the same air, but AM is much more sensitive to lightning and other static than is FM.
DSL service may be arrangeed to minimize crosstalk.
Because it's NOT just the wire to the farm, but ALSO other parts of the telephone plant being set up for DSL.
You could have broadcast quality microphones and loudspeakers and it will still sound like a telephone because of the limited bandwidth. Since bandwidth is limited, telephone components aren't high fidelity as it would be a waste to make them so. (I believe the modern "K" handset is clearer than the older "G" handset.)
Depending on the location, often times yes. Between central offices or within the CO almost always yes. I mean if you live across the street from the CO you probably have dedicated copper pair, but you live some distance you probably are multiplexed over a carrier line. The degree of multiplex determines your bandwidth.
What matters is the total price. When I got a car it came bundled with power windows, which I didn't want. Multiple dealers told me I'd pay _more_ to go a la carte and not have the power windows because it was a special order to them. So I got the power windows. (Turned out I like them. Sure, I could've hunted for a dealer who'd give me a better deal, but at some point the cost of the hunt would've exceeded any benefit).
Remember that while Henry Ford did very well at first, eventually General Motors and Chrysler surpassed him with their cars. They couldn't be the Model T on price, but they had better marketing. What was great in 1918 wasn't so great in 1928. Henry Ford was so stubborn he almost ruined the company and his family had to take it away from him. Even his wife voted her shares with the others and he was forced out. It's a shame such a brilliant man was also such an mean SOB. His "$5/day" wages was partly myth.
In many cases, if not all, the equipment is the same. Today voice talk is converted to digital for transmission, and those digital signals share the lines with DSL signals. I'd say the biggest investment (beyond more capacity) was in local loops so that customers could have reasonable speed on DSL. Not everyone can get it.
No, they're just easy to find laying around idle so one may take them and others will be glad you removed some old clutter.