It gives you more of a cushion for vacancy, repair, etc. 

Multi-units have better cash flow and more cushion for issues that arise.

Just jump in head first, and make sure you have enough of a cushion in the deal to put in an extra few thousand for closing. 

And, after renting both units, the mortgage and expenses would be covered with  some cushion on top.

Trying to invest in real estate right now would further compound this (IMHO very bad) decision.Why not... have you and her both save up like crazy for the next 5 years, and once you have more of a cushion, she can revisit the NP route? 

Lastly, having a larger monthly cash flow, especially on your first property, will make it easier to build up a cushion in your rental account for unforseen large repairs or vacancy.I'l quickly touch on an angle I've used while acquiring rental properties, especially those in poor condition or those where the price is already reasonable for what it is.

That and my wife's much smaller income would provide cushion and runway for future entrepreneurial opportunities, taking lower-paying W2 options that have higher long-term potential or are just more fun...and worst case scenario this would be more money to save and snowball....What I have to work with is about $200K in mutual funds and 4 doors (two 2-bed SFR owned free and clear each renting in the 600's, and a duplex mortgaged conventionally) that are all nicely cash flowing and gained equity in my ownership. 

So, if you are going to invest there, I think it best to NOT assume it will continue to boom as it has over the short term, make sure the deal makes sense today, and has some extra "insulation" to cushion you in case it goes bust so that you are not forced to sell or lose the property then.

The golden rule  to have a good cushion to absorb some sort of expense and loss.

How would that process work if it's not my actual house and all I have is a piece of paper.As Ryan mentioned, that's only going to work if you are under contract for a steal because they need that same cushion in order to make any money; if you are, why not buy it yourself?