Partial 1031 - New York City

[Krystal Ahn]

Hello,

I am planning to selling my investment property in NYC 

cost $721,000

est. selling price $1,000,000

mortgage left $350,000

accumulated depreciation $100,000

And buy an investment property with a value

$400,000

The remaining money I have I want to help to buy a primary residence which as my parents are getting older and I have decided to get a duplex (two-unit) house to have my parents live in the unit.

I have heard that it is better to do a 1031 with same or larger value and then to do a cash out refi ....

It would be great if you could help me figure out how much my tax liability roughly would be if I do this partial 1031 with much lower value. 

Thank you in advance!