We currently use a google spreadsheet that pulls in MLS info and Zillow info automatically and it auto-populates ARV using 90% of the Zestimate (I know...yuck...but it's at least a quick and dirty number that enables us to know if we want to dig deeper).  

I'd advise attending both and getting an understanding of the players and opportunities in MF in the area.

This thread was initiated not to agree on the best return metric but as an academic exercise to enable me to understand why the annualized return (IRR) goes down over time for a subject property I was analyzing. @ Stephen Greenway correctly explained that the decreasing irr comes from holding the property and averaging more modest and sustainable cash flow returns over the long haul bringing down the initial "flip" return. 

Loopnet is a good site to check the commercial players in those areas you are interested in....Then you can go to their iindividual sites, check out those agents that have the listings and contact them. 

All on Sub2, or is your angel investor enabling you to do cash purchases?

Financials must calculatePrefer 20 year mortgage termsWhat we (think) we need/want: Turn-key propertiesFavorable local market conditions and trendsLocal team of proven professionals (there seem to be      plenty of folks that are more marketer than player)Steady stream of rental income in 20 yearsFirst steps: Where should we be looking – Who should we be taking to?

At least that's what the big players said when I attended the NJ Multi family summit which was last October.  

Yes you can be successful without one, but the MLS is a major player in knowing your market and selling your houses.

Regardless of your ultimate ambitions, I'd encourage you to start locally and expand as your resources (time, marketing $, buyers, support team, etc.) enable.

Sorry I can't help, but I'll just reiterate my opinion on the importance of using someone who knows the players.