All weather package is basically heated windows (and I believe mirrors) and heated seats. Other than that, it's not that much more. It might also include the all weather floor mats.
I haven't heard the Kicker amp personally so I can't say.
My 2011 is my first manual car as well and boy, I know I've stalled this thing a lot when I started learning. I swear it was every other intersection that I stalled out at. It took a while to get a feel for where the engagement point was for the clutch. My clutch is also a lot harder than all the WRXes I have driven were. I always wonder if I have a defective or aftermarket clutch...
One thing to note is that second and third gears whine a lot when you let off the gas. My car also likes to jerk a bit when I do let off gas completely in second gear. Do not be too concerned if you hear/feel it. After test driving four WRXs (2 sedans and 2 hatches) from the '11+ revision, they've pretty much all behaved like that.