Am buying a 5 unit property for 400k and I'll need about 100k to close and then 100k to renovate.

I'm going to put this on a list of leading indicators/warning signs to keep an eye on.

I just started my due diligence phase, but the first thing I need to do is better understand the financial feasibility for the project, and how the return might compare to other investments we have undertaken in the past, which have been mostly acquiring existing buildings and renovating, not new construction.

I am relatively new to real estate investing and my goal is to start with a househack this year and scale my portfolio over time. 

I can't specifically help you with regards to Irvington, New Jersey but I would definitely recommend going to your local REIA group meeting and asking who other investors there use.

Say we buy a property for $1 million, but we structure it so it's 0% down but a bank/note buyer is in place at closing to buy the note from the seller at 80% value so they walk away with 800k in cash. 

Hi all, I have an office in a building where it will go on sale once the owner passes.

You now have a higher-value property that is ready to rent.Rent: Once the rehab is complete, rent out the property to generate monthly cash flow.

My gut feeling is next time this happens I tell the seller that I won't go along with such a situation.

I think I can get a policy online with the other requirements, but this waiver seems to be more difficult to find.