You are doing the right thing trying to get a handle on all of this before you come. BUT... just remember that what you hear over here WON'T be the same!! Similar to learning beautiful Oxford English, then heading to Scotland to work. Different areas will use slightly different structures, interrogative endings, and the pronunciation can vary wildly from place to place. "Shi bu shi" may be pronounced as "si ba si" or other forms depending on where you are. Different places will use an 'er' ending on words more frequently than others - yi diandian is more common here than yidian(r) (heard as yi diar), but friends here will call other mates Wang Junr (heard as Juar) rather than Wang Jun.
The gov't tries to teach standard putonghua in schools and universities, and there is some success. But - many university teachers will say to me, "My Chinese is very poor. I really only started to use putonghua when I came to university, and I still don't pronounce it properly". Shopkeepers and waitresses will speak local-hua (and if they come from out of the province, some of the locals won't be able to understand them properly as well!). The students who leave school at the end of their 9 years compulsory schooling (ha ha) will revert to local-hua - because that is what is spoken at home, by their friends and around them. Similar to the amount of French we learned at high school and how much we used it outside class.
I've seen universities with signs up encouraging both teachers and students to use putonghua rather than local dialect, but if there have to be signs - then it means that it is a problem.
A couple of my Shaanxi friends will refuse to speak to Gansu or Sichuan friends of mine on the phone, because they tell me the Chinese is too hard to understand!!
TV programs are quite frequently broadcast in local-hua as well, particularly provincial stations. I am told CCTV 1 has the most standard pronunciation, but some of my friends are highly critical of the word usage and pronunciation on the other CCTV stations. There is a reason most stations use subtitles in their programming!!
Older people, particular village people, will not always understand putonghua either.
It's a fun place to learn a language!!