Hi Jan,
The average temperatures in September range between 27-29 degrees, with night time lows of 19-20 degrees. Autumn is the best season to visit as summer months can reach 35 degrees and winter months can have lows of only 10 degrees. So I think september is a great choice!
Dress throughout your holiday will be casual. So baring in mind the warm temperatures, I would pack light comfortable clothing such as linen trousers, vest tops, shorts, t-shirts etc.
Cash is king in China, so it is best to be prepared and get your local currency before you travel for most expenses. This holiday is full board and includes all meals, transfers and excursions...so it is really up to you how much money you take with you. You will only need it for souveniers and times when you may choose to break off from the group and do your own thing.
There are ATM's available in all tourist areas and travellers cheques are available in most airports, banks, large department stores and hotels (hotels can sometimes give you better rates than cash).
I think your best option is to take cash with you, this way you can control what you spend and change it back if you dont spent it all.
I hope this helps, if you have any other questions, please do not hesitate to ask.
Many thanks,
Cheryl, your editor