When I was a newbie, I asked the top producer in the office if I could hold open houses on her listings.

I would want them both to still produce positive cash flow at the end of the day.  

She'll ask you to share your short- AND long-term goals, and once you have, she'll help structure a plan for you that will achieve those short-term goals in a way that should produce proceeds that will enable you to pursue your long-term goals.  

Currently I am personally looking to get some residential properties to accumulate a small-medium portfolio to both fix & rent (producing cashflow) and fix and sell.  

use it as a down payment for a more expensive income producing property?  

That property is still producing a 20-30% CAP.

Apartments do offer economies of scale, but you have to understand that the apt. market is red hot, w/ compressed cap rates, and generally don't produce as high cash flow return %'s on an as-bought basis as 1-4 unit properties.  

I don't really look at which one is the "most profitable" in and of itself but rather which produces the most passive income with the least amount of liability and daily involvement.The lending business is great because I do not use any of my own funds, I am in the safest part of the equity stack, the investor takes all the risk with the rehab, and does all the work. 

As an additional service, they will help keep your pipes clean with innovative drain maintenance products.

They have not produced any financials and the realtor is not sure they will.