Income tax liability of non profit AOP

Hello Sirs/ Madams Our mini residential complex has 25 flats in Kolkata. We are unable to get ourselves registered under the Housing Societies Act due to an issue with the builder/ developer. However we are interested to have a Bank Ac for managing our funds( maintenance/ sinking) for which we have applied for registration as an Association under the Societies Act. Our Association will be a non profit one with some charitable objectives. Now , my querry is: 1. What will be our Tax liability considering that we are non profit organisation and will be collecting only maintenance / sinking fund for running the complex. Our annual collection is around 6,50,000/ rs. 2. How do we manage to keep our tax liability minimum . 3. Do we get any kind of IT exemption? 4. Is it necessary to get registration u/s 12 Charitable for getting IT exemtions? 5. Is there any other way? Regards. Udayan Roy Kolkata