Buying a flat without OC in mumbai

Hi Im planning to buy a flat and the said building does not have an OC as of today 1.The project is a redeveloped project as the seller is an old tenant, he also is an advocate in high court. As per him with his discussion with the builder the OC has not come because the buidler constructed additional stack of parking of 3cars instead of 2 cars and due to the same OC is pending. 2.The flat is on the 1st floor, hence i dont see i will face any issues if he has constructed illegal floor, please advise 3. I want to know if i buy this property, can i be thrown out by the BMC or legal authorities from the said property? As the registration of Flat is happening. please advise. The old society is still functional which comprises of 18 tenants and no new tenant is added till OC comes & for the property tax for all the old tenants the same is paid by the builder . 4- I will be planning to sell the same may be after 5-7 yrs, do you think it will cause problems for me to sell the same in future? Please advise what all issues can i face now and in future Thanks