All of the information should be on www.wasen.de or www.cannstatter-volksfest.de which can be changed to English. Go to the tent (Zelt) websites, and they should have information about each tent. (You may be able to change it back to English, but some perhaps not. But opening hours and entertainment should be easy to understand no matter what the language is.) Typically, the Wasen opens at noon (perhaps somedays officially at 11AM), but not much will be happening in the tents until later. Of course, it they're open you can order food and beer. Just don't expect many people in any of the tents, but they all should have entertainment. Check them all out as it's really no fun to drink beer by yourself in a large almost empty tent. Some will have more people and be more fun. At 4PM things usually liven up as a lot more people arrive, but most reservations will not kick in until 7PM. You're free to sit at a reserved table until the reservations kick in, but its best to try to find an unreserved table so you won't have to give up your table.
Wednesdays are family days with reduced prices for the rides. I don't have a calendar handy, but 3Oct is a national holiday, and it will be much busier, as will the night before it. Oh, Thursdays are also a fairly busy night.
At the moment, neither website appears to have an English version. You want to look at Festzelte for the tents.
Edited: 7:37 pm, November 21, 2012