Business trip/Exhibition trip to Shanghai, China.

Good day, My company is interested in attending a conference/exhibition in Shanghai, China in May and I would like to get some information regarding visa requirements. Firstly, how long does the process usually take (how far in advance should we apply). 2) Do we need a letter of invitation from the organisers of the event and if we wish to travel outside of Shanghai for a day, will we require any further information and/or entry permits. Lastly, do we need to provide personal and company information for our attendees or just their personal info? Thanks in advance for all your assistance regarding this. Look forward to hearing from you