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.

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?

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)..

If you want to do this right you really need to be working with a local attorney to the business and property who is an expert on mergers and acquisitions, entity creation, and business real estate.Trust laws and all of that varies by state.

Scale is usually achieved at 75 doors or more in size.

As you scale up, you'll find it's easier to stay organized with more automated systems. eRentpayment has auto reminders for the tenants, options to allow/not allow partial payments, notifications when the rent is paid and by whom, options to allow utility and security deposit payments, thank you notices, etc.