Buying a resale property that is unregistered through 3-party agreement

Hi, I have shortlisted a resale(ready-to-move) property which I want to buy but it is unregistered and it's 6 year old property. Also its a loan free property. The broker tells me it will be a Tri-party Agreement for Allotment Transfer and is very common where Builder, Buyer(Me) and Seller will enter into agreement and Builder transfers all his rights to me by some nomination or endorsement or something like that if I remember well. However I want to make sure if this is safe? 1) Is it Safe to Buy such a property that is Not registered yet by entering into such 3-party agreement where builder too is one of the parties? Or is it always safer to buy resale property that is registered? 2) What All Papers I must check in this case if I am going half percentage for bank loan and other half buy it from my own fund? 3) Will the Seller need to be present later when I want to Register the property? 4) In case I go for Bank loan will Bank make their full payment at time of this 3-party Agreement? And will the bank disburse the amount to me or directly to teh owner? 5)when can I register the flat? Can I do it before paying the full amount? 6) Is it okay to not get the property registered after buying? Is there any option as such? Kindly suggest. I don't want any hassle or later problems while registering. Thanks,