Firstly - the holiday was one of the best I've ever had. There were 32 of us but not all took the the add-on option. I just want to add a few tips on making the holiday a little easier.
Take a large case which is virtually empty as you will be doing a lot of packing and unpacking and then there's the shopping... I urge you buy the silk duvet (and pillows) at the silk factory. They pack it tightly so as to fit into your case.
There is a train trip to Chengde where you will need to take enough provisions for 2 nights, 3 days so make sure you take an extra case/rucksack as your main luggage remains at the Beijing hotel in a safe place.
You have a 2 hour drive back from Chengde before flying from Beijing (where you will be reunited with your case) to Xian. A packed lunch is supplied and you have time to remove anything from the Chengde trip and put back into your main case.
No need to take a kettle (which I did) as there is a kettle in every hotel but you should buy a cup for the cruise (unless you upgrade). There was a healthy mix of upgraders and non upgraders. Should you upgrade you get a dressing gown, different food in your own dining area and free laundry. You also get free wine and beer. The add-on is the best decision I took as the holiday is very very hectic and you get a chance to wind down.
It's best to get as much Yuen as you can before you leave or take Pounds as I didn't get to see an ATM till Chongqing and the boat only takes cash. You sign for everything and then pay at the end of the cruise - I used my debit card for that and any other big transactions i.e. optional excursions. There is a 15% service charge but you can still leave tips for the cleaner, waiters etc.
There are more 'squattie' toilets than western and make sure you have toilet paper/tissues with you at all times.
Regarding accommodation my personal opinion is the first hotel in Beijing is the best, Chengde has the hardest beds and people complained about the cold rooms although I slep like a baby. Xian was good but my favourite was the lovely little cabin on the 2nd floor. Watching the river from my balcony in the early morning was sheer joy.
Anyone going will have a brilliant time as its a real adventure. I had the time of my life.
Enjoy.