Yes, it is more easy and comfortable to take airplane to Jiuzhaigou from Chengdu, for it takes 10 hours by bus. Jiuzhaigou's low season is winter and hot season is Autumn. It will be quite since late Spring to Early Autumn. Oct is the best season to see Jiuzhaigou. I have no idea about the English guide and if possible, I think you should consider to jion a tour, like 3 days leisure tour in Jiuzhaigou. To get around Jiuzhaigou, Huanglong area, it is better to rent a vehicle. For senior people like you, that is more easy to have others arranger this for you in advance, including hotel booking, car and etc.