The term "local pay" is a red flag. The average monthly salary for professional workers in Shanghai is around 5,000 RMB, which equals roughly US$700. It is very unusual for any professional salaried employee to receive over 10,000 RMB per month, whether they are lawyers, doctors, or IT personnel.
Before considering a move overseas, you need to be presented with an offer and proposed contract in writing. The contract should state the proposed duration of the assignment and its terms.
The contract should provide for your normal salary (US$70,000?) to be paid in US$ to your US bank account. In addition, you should be given a foreign living allowance paid in local currency to your foreign bank account. Getting your regular salary deposited into the US is critical because foreigners face legal restrictions regarding repatriation of funds out of China.
The average cost of living in Shanghai is easily 20,000 RMB (US$3,000) per month for a typical ex-pat living alone. Double that if you have a wife and kids. Obviously it will cost less if you do less, and cost more if you do more. A quality 2 bedroom inside the Inner Loop, but not in a premium area, will run 6,000 - 9,000 RMB per month.
You will need to get a Chinese work visa sponsored by your employer, as you cannot legally work on the typical "L" tourist visa. You will also need to register with the Public Security Bureau upon your arrival. It is just a formality and never a hassle. You will need to file income taxes in China and the US. China takes a flat 20% income tax.
Frankly, your employment offer sounds very, very vague. All of the offer details, especially the financial details, need to be presented in writing. Shanghai is an expensive city, so get your details clear.
5 years in Shanghai