Capital Gain counting and Tax Exemption

Couple of questions around counting Capital Gain Tax: 2009-10 : Purchased Apartment and Agreement of sale was done. Flat Number was given by builder. Consideration of sale on the agreement is : Rs. X. 2012-13: Construction finished and paid the registration fees. Stamp Duty was paid but it had different consideration of sale: Rs. Y (which is almost half of Rs. X). Also, spend money in furniture and modular kitchen. Now, I have plan to sell off the apartment in May-2017. 1. Shall Rs. X or Rs. Y be considered for calculating the indexed cost of acquisition? I actually paid Rs. X for the flat? 2. Shall the amount paid in furniture and modular kitchen also be considered and indexed? 3. Shall the interest paid to the bank before taking the possession in 2012-13 be considered in cost of acquisition? 4. Which index shall be taken into account for cost of acquisition, 2009-10 or 2012-13? 5. If the long term capital gain is almost zero, then is there any mandate by the government to use the capital gain or sale proceeds in a specific way? or it can be used to buy even a commercial property? Request all the experts to jump in and help me. I really need help !!! Appreciate it !!