Travelling from Australia to China - VISA Question

Hello, we are travelling from Australia and have a question. Our itinerary; shanghai 4 days, beijing 5 days, xian 2 days, guilin 3 days, hong kong 3 days, macau 3 days, shanghai 3 days. Do we need a multiple entry permit? OR; can we buy single entry and use the 'free visa' for when we return to Shanghai? Thank you.