You don't want to get a call 3 months into a project where you have lent money and hear the operator say that they ran out of money and need more money from you to finish the project or you will lose your investment.

It seems not the best way to spend money.

When I was 19 I was washing dishes out of high school in Columbus and then decided to buy a single-family rental.

Value your money more. 

My plan is to buy the house subject to their existing mortgage, renovate the property, refinance it and pay off their remaining loan balance using the money from the cash out refinance.

If you have a chunk of money to get going I'd personally buy the biggest thing you can if you don't I think house hacking into a 4 plex is great. 

Once your emergency account has a reasonable amount in it, whatever that means to you, you might want to think about steering that payroll money into the investment savings account from each pay check and leave the emergency account money as is.

I would like to put the money into purchasing another investment property.

Going direct instead of having a GC do the work will save you money too since that GC will put a percentage on top of work. 

He's an educator and does make money selling education, but like most of the others doing this, he began by doing deals.