History has proven a small determined group of people can be a constant thorn in the side of a larger, more powerful foe. We never saw the entire rebel fleet until Return of the Jedi, so it's clear there was more than one base of operations.

A powerful WWII vessel could be sunk by a well timed torpedo or bomb drop, so the DS getting blown up isn't that much of a stretch.

Allowing the Death Star to track the Falcon was an attempt to lure the battlestation into a vulnerable situation, away from the rest of the Imperial fleet. (And bank on Tarkin's overconfidence.) The window of opportunity to exploit any weakness found in the plans wasn't going to be very long either way.