#4
9 gauge strings for classic rock in standard tuning is pretty much the norm.
...:::The Master Chief :::...
#5
The lesson portion of this web site has a detailed explanation. Tone and longevity are the main factors. I personally like lighter strings because it seems like you can turn the action down without fret buzz a little more.
#6
10s to 11s perhaps. Heavier strings have darker sound to it or just....heavy. But fretting those strings may be a little harder than fretting 9s or 8s.

All depends, changing string gauges might mean that you'd need to adjust your intonation, action, also your truss rod. High string gauges (12s, 13s) most likely associate well with drop tuning as it wont put up as much tension as regular tuning.
"Play with your ears" - Yngwie Malmsteen, Paul Gilbert
Thats what she said...
UGmusic