What is your comfort level? 

And try to master those taking as much time as you need to be comfortable with it.

If you want more, you buy more at a pace that is comfortable for you.

It might be that this couple that owns the house is just getting their feet wet with having someone else managing the property and they want to get comfortable with your management style as being what they want.

The key is understanding your comfort level with managing multiple units right out of the gate.. 

When you buy a property with the intention to Airbnb Househack, you can find a better layout to make it more separate / private but start with what you have, Get temporarily uncomfortable so that you have a comfortable future.

My grandfather used this truth to subdivide & sell most of his farmland in rural MA and sustain his family comfortably over the years.  

Unit 3 - mid-term rental (this would be best for the most private unit as most mid-term renters are more concerned with privacy and creature comforts than amenities)4.

Get out of your comfort zone.

If you’re working with VA-savvy lenders who are comfortable with your plan and don’t impose stricter rules, you might be able to rinse and repeat as you described.