yes, the letter from chamber of commerce is compulsory, if you don't have it, you can't get a business visa to China. I don't think you need to change it to businessman, but if you still have worries, just renew your passport.

Do I need to purchase the actual ticket when applying or itinerary is sufficient?

You don't need to purchase the actual flight ticket when you apply for China business visa, the visa notice sheet from the chamber of commerce(or called invitation letter)is the most important document, if the flight ticket is required, the visa officer will ask you to show it when you pick up your visa.