subject to real estate deal from entry to exit plan

[Yangchen Dolkar]

Hi! BP friends,

I'm located in New York, Queens area. I'm first time home buyer. I met with a seller who is willing to do 'subject to' to sell his 1.7 million 4 family house but we both don't exactly know how does it work. he has around 600k on loan and because it was his 1031 exchanged house, he's gonna be paying a lot in tax. 

My question is when I take over his loan of 600k, how can we work with 1.1 million? 

and when he files tax, how he gets taxed? 

If someone can give me entry and exit plan for this deal, i will highly appreciate. I'm sure theres so many things I may not be aware of for subject to deals. any informations you experienced people give me. I thank you in advance.