2. Uncertain. Someone will have to test that behavior to find out.
3. It depends on what you pass in as a parameter to GetWeather(). You can pass in either area or module to determine their weather settings respectively.
4. From my own testing, I think so, yes (I've never messed with weather and it has always been sunny), but there could be default values in area/module properties (I didn't see any but I wasn't exactly looking for them either).
5. Take a look at SetWeather(). Pull it up in the script editor (functions tab) and click on it for a brief explanation of what it accepts and returns. It seemed pretty straightforward from what I recall, but there's no substitute for testing things out in game.
Should curiosity get the better of you and you find it impossible to resist the urge to play around with NWN2 weather settings, please let us know what you discover.
