The down payment is 25% down for single family residences and 30% down for 2-4 units.

I could put a down payment for a conventional (20-25%) 550k duplex, but I feel it could hurt my chances of buying as many duplexes in a 5 year period (for example) if I go conventional VS an FHA at 3.5%. 

He wanted 1/3 payment up front in cash and I paid him.

Option 1 - NOI = Rent - (maintenance, vacancy, management, property tax, insurance)or Option 2NOI = Rent - (property tax, insurance)in both cases i assume DSCR = monthly payment/NOI

I agree with Erik, although their are some investors out there that will help fund the down payment/entry fees that you mention, they typically are friends and family that trust you and believe in you.

Can I get a loan for the down payment / construction costs2.

Looks like Paramount is under Federal investigation for having failed to make agreed payments. 

All interest payments flow back to the Roth IRA and HSA tax-free. 

There are significant details that I'm choosing to leave out regarding rent payments and balance left for the owner as you terminated the lease early. 

sm IS LOADED WITH FAKE LENDERS NO LENDER IS GOING TO WANT A PAYMENT THROUGH PAYPAL FULL STOP.