My first several properties were vacation rentals, and I used the cash flow from those to scale into 22 LTRs and counting.

Let's also assume this plays out across several properties, so we can safely utilize a market cap rate of 7%.Assuming your building is identical in terms of unit size, quality, location, etc - You have 14 units with market rent of $1k/mo ($168k/yr PGI). 

I currently have a house listed on Zillow for rent and I have had several applicants who don’t meet the criteria, yet still are insistent I should rent to them.

It could be a good deal, but the odd things are there are several containers stacked in the front yard.  

My first go-around w/ the 4 unit involved a very primitive understanding of due diligence and not really calculating any specific reserves.I know I own and have listened to several books that touch upon it (HOLD, ABCs of Real Estate Investing) but having them in just audio format has make it a bit more difficult to find the right information if they are in there.

What we read over several blogs is,1. if we have to take out plumbing and electrical permit, we have to have a building permit2. if we ourselves take out permit then we are responsible for all the work and insurance etc.I will definitely call the building dept

The listing was on Zillow for several months with 2 price drops.

Even if it takes a couple more months to get a good tenant in it cost a lot less than a none paying tenant for several month, court fees and rehab fees.If she cant pay 1st last and security right now she most likely isn't going to be able to come up with it after she gets in. 

I doorknock on a regular basis and have several leads for flips but no team in place yet.

This home you need to re-carpet the homes in several rooms I doubt it costs you just $1500.