Rental Acquisition OofO - Pay in full or take mult mortgage?

[Josh Merrell]

^ that's order of operations in case no one knew what I was going for ^

I'm looking for some advice from those of you who have multiple rental properties. Thanks in advance~

We bought our first rental condo in full last year using our savings and a family gift (yes, fortunate us). Since then I've been getting a feel for the ins and outs of mgmt as well as how to determine a reliable roi when looking for additional units. 

Just this month we closed on a second comparable condo, with 20% down to avoid mortgage insurance.

Here's my big question:

Should we now pay our future savings toward paying down the remaining 80% asap, or should I continue on toward a third condo with another 20% down, immediately renting it out and covering the mortgage payment, so on so forth... 

In the end I'm aiming to continue this game for the long haul, not interested in selling, only acquiring. 

Factors I'm aware of that might help determine the most efficient answer:

-tax writeoff of interest portion of mortgage payment (most impactful during early years of mortgage) 

-margin of net rental income after all expenses 

-ability to qualify for attractive interest rates on additional mortgages

Basically I'm just trying to get the most bang for my buck. If I take several mortgages out simultaneously, I'll be bringing in small net margin for each property earlier than if I'm waiting to pay in full, but I'd like to hear from others whether the extra work dealing with the loans and mgmt of everything is worth it. Thanks