Residential and commercial

Sir, In a registered agreement, the place is written as flat, but the seller is saying u could use this flat for both commercial and residential purpose and also says that he has a copy of plan wherein the structure is given both residential and commercial status (it's a redeveloped registered condominium) and it's not proposed under maharashtra state cooperative housing society as yet. Before getting into agreement what r the prerequisite to be fulfilled in order that I could enjoy both commercial and residential status. The thing is that it's just a word of mouth saying, 1) What documents should I receive from the society and seller (for both business and resident purpose) at present, so there is no problem in near future 2) My future plans is to open up an agency business there. 3) Does the approved plan which the seller mentions would assist in getting the NOC for opening up of business. If yeso, how to use it? Please give the feedback.