Information on requirements of an invitation letter and accommodation

Dear Sir,
We are South African residing in the UAE at the moment with working visa's for the UAE.
We want to travel and explore China during the summer holidays for three weeks.
We have not booked any accommodation except for the initial stay in Hong Kong on arrival.
We do have the essential outline of our touring plan but we prefer to go on recommendations from
local touring companies and information from the local people themselves.
We have not been invited because we don't know anybody there except for some
teachers, but do not want to bother them with our visit as we are not close friends
Is the invitation letter essential and is the accommodation reservations in advance essential
for the issuing of a visiting visa.

Antoinette De Bruin