Well.. I want to attach a question... do you feel 普通話 is the easiest chinese language to study? I say it because I found 廣東話 and 閩南話 has 8 tones, as well as 四川話 which has more than 5 tones.

In Shenzhen they speak Cantones, in Fujian they speak Hokkien (Also named as Min), and in Shanghai, they speak Shanghainese(a variety of Goetian, goetian is also named as Wu). They are different languages linguistically. None of them is dialect of Mandarin.

Yes there are 8 main dialects Stem from mandarin. Besides there are some,minority languages out of HAN Minority.

in Mainland they speak Chinese, the official language of China in Shanghai they speak Shanghainese in Shenzhen they speak Cantonese about Fujian -- no idea, never been there whether to call them languages, dialects or regional varieties -- as you wish

yes,,,,In the past 700 years ,,,Beijing is the capital,,,as the center of China,,its language is most powerful ,,,, Mandarin came from Beijing's dialect.And Nothern China 's main dialects are similar with Mandarin . Shanghai and Fujian,and Shenzhen's,,,of course difficult,,,,,,but they can speak Mandarin,,,,,