Raven,
Lots of useful info here I think. For me, the two best bits relate to the uncertainty of forecasts:
1. As MG says, get some dual experience of "bad weather" flying - it is amazing to me (now with a bit more experience) how low-time PPLs do not see the pretty obvious signs of in-flight weather deterioration and take the necessary steps;
2. Do what you can to improve on the forecast: definitely talk to yoour arrival site if you can, and any obvious alternate
BUT also do not forget, you are flying a helicopter: if you do not like what you see in front of you, and YOU are wishing you were not up here - LAND.