If its a duplex, odds are in your favor that both units wont go vacant unexpectedly, however if its a single family and it goes vacant, I would tack on an extra month since you wont be getting any rental income. 

@Joseph SkatesI'm not sure I clearly understand your question.If your business is collecting waste then you will most likely have a couple of possible revenue streams: a dumping fee you may/may not charge to folks who bring the waste two you;scrap fees you may collect on sale of the various component elements you extract from the electronics.Depending on where you are, there may be a provincial program which will supplement one of those revenue streams (kid of like the tyre levies charges my many/most provinces).  

The 2 main components of wholesaling are marketing and having a good buyers list to flip the deal to.  

My mortgage to income (>40 of my income was going to my mortgage) would leave very little room for fun items or unexpected expenses. 

We have regulated the components so strictly that it's very challenging to acquire them and they usually cost more than the meth you could make would cost.

With any real estate investment, there are going to be unexpected capital expenditures at some point down the line and you have to be prepared.

However you would need to prove that you had some kind of unexpected life altering event like a job transfer to another state, etc.

There is probably a component of landscaping that was done incorrectly around the garage creating a flooding scenario.

unexpected vacancies. 2 were at market rate, so that sucked.

Generally more, however this accounts for any unexpected bills or situations that arise during this time.