I use dual monitors with my ATi no problem.
Granted neither of my monitors are DVI connected, so I use the DVI > VGA adapter.
The way it works is that you configure Display Manager to extend your desktop (not clone) to the other screen.
IL2 will show on your main screen, and anything you have dragged to it will show on your second screen (including task bar ).
I have not noticed any performance affect, and it is nice having a map, or TS or whatever showing on the secondary screen.
So:
a) Yes I believe so.
None
c) You can have maps/porn/TS Client/flight instruction manual showing on 2nd screen.
Also for day to day stuff it can be very handy having a 2nd screen, when I work on PHP files or other coding I find it invaluable.