A buyer could ask you for the original Sale Deed, Title Deed, relevant tax receipts and Encumbrance Certificate.

There are a few exemptions available for long term Capital Gains, if you Buy or construct a new house: If you build a new house or buy one from the money you receive from selling a property, you are exempted from paying the tax on Capital Gains. However, the new purchase should be done either one year before or within two years of sale and the construction should be completed within three years from the date of transfer. The new property bought or constructed should not be sold within three years from the date of its purchase or date of completion of construction.

Yes. Generally, the stamp duty on the gift deed ranges from 5% to 12% in all states. In few states like Haryana, Rajasthan and Delhi, concession of 1 to 2 per cent is given to female transferors.
Can I authorize someone else to register my property by granting him Power of Attorney?
Yes, you can execute Special Power Of Attorney to get your property registered by someone else.