Going full time with $50,000 in 4.5 years

[Andy Hathaway]

I plan on leaving the active duty Air Force in 4 and a half years when my enlistment is up. My goal by then is to have 20 units that average at least $300 in monthly cashflow so I can be a full-time investor. My credit score is hovering around 800 and I have $50K that I have dedicated to start buying properties. I've been educating myself on everything REI for over a year and am ready to hit the ground running but I'm having trouble figuring out what my focus niche will be. My only debt is my 4 bed 3 bath home in Dover Delaware where I live that I'm currently renovating and will cashflow ~$300 when finished. My questions are:

1.There are so many options and niches out there, with the goal of 20 units in 4.5 years in mind, do you think focusing on single family homes using the BRRRR strategy is the most efficient? Should I be looking for something larger perhaps with a partner? (Multi-Families in my area are seemingly scarce)

2. Do you typically find that you get more bang for you buck buying 2 properties at say $80K each rather than one at $160K? If so, is the additional cashflow worth the additional time managing them?

3. If you could go back in time, what advice would you give yourself before you bought your first property?

I look forward to hearing your thoughts!