How many units/Properties a year is realistic?

[Mark Voionmaa]

Just started to invest and rehab last April 2017. To date I have completed a duplex and a single family. Just purchased my third property, which is a single and should start renovation in the next month. 

So far, I’ve been buying properties that need a lot of work. Duplex took 5-6 months to complete and single took about 2 1/2 months. So have gotten 3 units running in a year.  My strategy is to give a nicer apartment than the typical one in my area (no slum lord) and get a little more monthly rent. So far excellent results. Buying in C class neighborhoods.  

My goal is 30 units to be able to quit my day job. What is a realistic timeframe to get to that number while doing it right. I have limited cash so can only do one property at a time as I have to refinance each property so I can get the cash back to be able to purchase another property. 

ROI has been 15%, 12.5%, and 10% respectively. Am I being too picky?

Thx

Mark