I plan to travel to Jiuzhaigoa & Mt.Emei in Oct, is that a perfect timing.

Perfect timing to visit in October for the weather and scenery is good but it is peak season and many tourists there at this time. It is the National Day Holiday from October 1-7. Better to avoid this period. The temperature is about 12-20 degrees in early October. It may rain, because it is really hard to say. Need to bring warm coat for the temperature varies greatly at daytime and night. Not necessary to bring sweater yet. Huanglong is open is tourist in October. You can also visit the Leshan Giant Buddha which is not very far away from Emei.