Hi Kathy
I did this trip (not the Hong Kong add on) in October 2014 - if you type China into the search facility at the top right hand corner of the page you will find loads of reviews and tips from people like myself, Mike W and Bob Grey who have done this trip (and loved it!) and which will probably answer most of your questions.
I would suggest taking some Yuan to start with but most of the hotels will change sterling if you need more (however - your sterling notes must be in pristine condition or they won't accept them). Credit cards are certainly accepted at the larger places and outlets (such as the silk and jade factories that you will visit). The only place that definitely required cash, from memory, was the Chengdu Panda Research centre. This was for the Panda Keeper Experience option which was around £200 but I'm sorry to say that Julia has confirmed in another thread that the 'Panda Hugging' session is no longer available due to infection concerns. Such a pity for you as this was one of the highlights of my trip (if not my life!)
In terms of shoes - take pairs that are comfy for walking as you will be doing a lot of it, including on cobbles (the Forbidden City) and steep slopes and steps (the Wall). Take layers as the temperature can vary wildly, especially if there is cloud (i.e. pollution/smog) cover. Also take plenty of wet wipes, handy packs of tissues and/or toilet paper (facilities...vary...) and throat sweets. If you use inhalers, take extra as you will need them more than usual due to the air quality.
It's a full on tour but you will have a super time and the hotels are all excellent.
Happy to help with any other questions
All the best
Mandy