higher gauge strings usually have a thicker tone, but are harder to play. If you guitar was set-up with lighter strings, and you move to a heavier gauge, the increased tension will require you to adjust the "truss rod" of the neck to compensate for the bow in the neck, due to the increased tension. You can google "truss rod adjustment" to find lots of information on that if you need to. Otherwise, if you have a very expensive guitar, or are not comfortable doing this (even though its not really that hard, and you wont mess anything up if you adjust in very small increments and don't force anything) take it to a guitar shop to get adjusted. Its only like 15$ here or something
Good amp settings...Well it all depends on the guitar im running. As a basic rule, I usually put my EQ all at 5 (middle) and start from there. Some other people should be able to help you more with this. What amp are you using and what guitar?
The tone dials cut off high end I think...if you roll them down you get a "fatter" tone.
d) lets use a strat with 3 single coils for example. The neck pickup, due to its position on the guitar, will have a rounder, fatter tone. The bridge pickup, since it is close to the bridge, will have a more....chunky? tone...
take an acoustic guitar and strum near the neck...the sound is fuller with more lower frequencies. Now, strum right near the bridge, and the sound will be thin and weak. The neck pickup is traditionally used more for soloing on an electric guitar, whereas the bridge pickup is traditionally more for rhythm. This is all relative though, as a lot of time I use my bridge for soloing haha.