Inheritence of property from mother

My mother has bought a flat in her sole name in one of the residential housing projects at Kolkata in the MIG-U segment(the project is a joint venture between a company & WBHIDCO) in which there is a income upper limit. My father has died few years back(before the apartment was purchased) & Iam the only child of my mother & iam married. Now my questions in this aspect are the following: 1.In case my mother dies post registration of the property,do the income eligibility criterion which was imposed before allotment of the apartment(as mentioned above),can be imposed on me by the developer,before transfer of apartment in my name. 2. Do my mother needs to execute a will in favor of me or post death succession certificate is sufficient to establish my sole claim on the same(and tell me at all if i require either of these as iam the sole heir for her) or there are generally provisions of any nominations now. 3.Which one is more cost effective the will now or succession,if either of them is a requirement. Waiting for your suitable & professional advise.