My friend said that they go through OG questions in the class room. Then assigned
MGMAT books to finish chapter wise and alongwith each chapter advised to finish related OG questions. So if you have doubts related to OG or
MGMAT books that will be mainly discussed in the class. Apart from that you are assigned 30 minutes per week for doubt removal for any questions. So if you think you do not go beyond
MGMAT and OG questions, then in my view you better buy all these books and finish each chapter of
MGMAT books then finish related OG question and similarly go on. This way you essentially chart your own course at your own pace.
A word of advice, if possible arrange a buddy to study GMAT with you. It will really help. You both can even speak through GTalk or Skype and don't have to be at same place. Only thing is that you have to have same study materials.