I am narrowing down a list of potential 3-4 unit residential properties for my first investment. 

However, my experience with conventional mortgages is that the lenders have a very narrow set of criteria that you must meet.

Also if you're wholesaling properties from the MLS you're not really adding value to the transaction, it would be like selling band-aids outside of a hospital. 

Also would it make sense to just narrow which area of REI you're willing to help with (flippers, buy + hold landlords, wholesalers, whatever else)? 

But I would suggest narrowing down your area of the city you want to focus on and look for vacant properties, network with other real estate investors, and try not to get caught up in "quick money/wholesaling is easy" thinking.

I am the balding guy with the ponytail (consider banding up scalp!).  

hi Lee,This is going to be a difficult answer for a data nerd, but you aren't going to be able to get super granular about maintenance and cap ex without defining a narrow asset class.

(although many do), I'm saying all A, B and C areas aren't created equal.  

I think the 50% rule makes a lot of sense for MF in B and C neighborhoods.

If cash flow is what you are seeing, typically B and C type neighborhood (sometimes at the cost of s***ty tenants) can cash flow well.Of course these are gross generalizations.