Capital gain if buying a house first and then sell old house

Hi there,

I have a 2BHK house, say  House 'A' in Pune that I jointly own with my Wife where I am living since 2012.

I also have anotyer  2 BHK flat in Pune, say House 'B'  on only my name , purchased before I got married, which I got possession in early 2013-its loan free.

I want to sell any of these 2 Houses, depending on which one gets sold first, and use the amount to buy a larger  house in Pune, say House 'Z'.

I have already decided on the House I need to buy.

1.However, If I first buy this new ready possession house 'Z',  first  in Feb 2018 and then sell the old house once I get a Buyer for it, will I incur long term capital gain even if I use the proceeds of the gains from selling House to pay off Loan for new House? 

2.Do the Buying and selling have to conclude in same Financial Year? 

3.For avoiding Long Term Capital Gain tax, do I need to first sell and then Buy or I can do vice versa?

4. What are the options avaible for me to best make use of Income tax LTCG in this scenario to save tax?