And what are the key ratios/metrics I need to pay attention to in order to determine whether or not the investment makes sense.

The key to everything is your CC&R's (Conditions, Convenants & Restrictions). 

I am in nova too and just like you started in Rei space last year with two turn keys under my belt.

Change all the locks at that time as you never know how many keys to the place are really still out there.3.

I had them re-key my other properties so its part of their system, so I don't even need to worry about leaving keys. 

Fill in the foundation below.Check out the Start Here page http://www.biggerpockets.com/starthere Check out BiggerPockets Ultimate Beginner's Guide - A fantastic free book that walks through many of the key topics of real estate investing.Check out the free BiggerPockets Podcast - A weekly podcast with interviews and a ton of great advice.

Fill in the foundation below.Check out the Start Here page http://www.biggerpockets.com/starthere Check out BiggerPockets Ultimate Beginner's Guide - A fantastic free book that walks through many of the key topics of real estate investing.Check out the free BiggerPockets Podcast - A weekly podcast with interviews and a ton of great advice.

"Returns around 4-5% are for turn key properties... if that.

The property would therefor have almost no cashflow during those 4 years(I know, I know cash flow is key, but this is kind of a weird situation).  

It is just one part of the decision making process and one that will help somewhat in comparing one investment against another.Using leverage is one of the best ways to create wealth and the key to doing it successfully is to learn how to manage risk.