Pick their brains, their successes and their failures3) Take Action: Save capital, evaluate deals.

Im considering my first MFH and as I'm evaluating the deal, I realize I'm not sure how to get a comp or an ARV.

First step is a very rough estimate to see if the property is worth evaluating further, next is a detailed estimate on your own when you go out to view the property if you do so that will decide if you want to make an offer. 

I am just trying to evaluate options to keep the low monthly payments and at the same time update the building to keep it.

Then just evaluate the deal like you would any other rental property. 

How does one compare the price between a sfh and a duplex with the same square footage, and finishes in the same neighborhood?

The goal here is to analyze the value of a duplex surrounded by SFHs.

Should I expand t...

Maybe that is bird-dogging deals once you learn how to evaluate deals, maybe it is cleaning up their flips/rentals, etc.

It was quite common to use Comps from one subdivision when evaluating another. 

3) how can you evaluate these deals to ensure cash flow with mls data, if possible?

You would evaluate your holding costs at the much cheaper FHA 203k interest rate or conventional loan interest rate, if you wanted you could inflate your return by assuming you would have paid $x in rent per month as well other than that it will be pretty similar.