Rental cash flow vs down payment

[Alessandro Struppa]

All,

What is the ideal cash flow per unit for a specific % of down payment? I’ve watched numerous webinars and 100$ to 200$ seems to be the number. My question is what % down payment should be giving me that cash flow? Of course if I go 80% down my cash flow will be very different. Also.....Would it be better to invest in a duplex at 40% down or 2 duplexes for 20% down each? Considering they are exactly identical and produce the exact same cash flow. Sounds to me 2 duplexes would be better as both would be going up in value compared to only one. 

I am new to real estate investing. Just purchased a single family as a rental property and now looking into duplex maybe 4plex. 

Just trying to understand how to analyze my deals properly.

Thank you!