We are going to shoot for buying 2 SFR's in 2016, and scaling up from there. 

The financial issue arises when one wants to scale.

Especially when scaling and building your business.

If you truly want to work on your business and scaling it for future demands and success, definitely take some time to entertain the idea.

Each reasonable set of applicants should be graded against the mean of who is part of this micro set, applicable to YOUR market.

These tools suffer to scale very well, which means that as you grow your business you will find it increasingly difficult to manually input sales leads, employees, contractors, accounting, business processes, and so on.

Do you know of anyone doing this on a large scale?

I probably could've saved at least $10k or so if I did a rental grade product.

On the growth of your operation...Probably much depends on your circumstances and lifestyle..of course, you get economy of scale with multiple units in one structure (one mortgage, one insurance bill, tax bill, one roof, one lawn, one parking lot/driveway, etc), so a fourplex  gives you even more scale than the duplex (or your question may even be about 5 plus units)..

Please tell us more:Is this wall in a basement or above grade?