The easiest way is to take a plane to Jiuzhaigou at Chengdu Shuangliu Airport. But it is more expensive. Or you can take a bus to Jiuzhaigou. You can take a bus at Chengdu Xinnanmen (New South Gate) Bus Station, Ximen Bus Station or Chengdu Chadianzi Bus Station. Remember to buy your bus ticket in advance.

You needn’t worry about your lodging. You may find many hostels near the entrance of Jiuzhaigou.

There are not so many hotels open during the winter around Jiuzhaigou. There are a few expensive places like the Sheraton (probably good discount) and a few cold Chinese hotels! There is an Intercontinental as well. You can fine their information on the internet. There is also a home stay that I believe is open all year around.

how about the weather/temperature at that time in February, march?

The temperature in 5 days is from -5℃ to 15℃. It will be cloudy.