Snowball affect best route single home rentals

[Jorge Leon Jr]

I am new here and want to hear some opinions

My goal is 100 rentals single family homes in 10 years looking at a 8-10% ROI after factoring in a 40% cost factor (vacancies, repairs, etc)

My example is (12 months of a 1250$ rent x 60%)( divided by cost of home 100k) = 9% ROI)

My main concern is how to snow ball and pay down the houses

Or save up and pay cash on homes on each purchase

Or equity loan to buy out right and repeat

Or pay off 1st/oldest loan asap and buy more with another loan cash and repeat

I run a restaurant making above 100k income

Above 150k combined with my lady

I know i have many routes to get there on how much i can pay down or save up yearly and pay cash

Any opinions 

Im in south texas and would like to stay local and in my backyard i would get C and B- nieghborhoods that i know

More then likely once past the 50 single homes ill be stepping slowly into multis afterwards

Thanks in advance!