Unfortunately, both of those results are unlikely to repeat, and neither are anything close to sustainable.

Advice for this site...1) Set up keywords for your area and interests so that you're notified when they're used and then start interacting. 2) Read through The Ultimate Beginner's Guide3) Go through applicable blogs and podcasts as there are a lot of great resourcesAdvice for REI...1) Study up on what you need to know/do for the 1st step and then do it, then repeat for all following steps until you have completed your first investment then repeat process and keep learning.

It sounds like your biggest problem isn't the early term it is the repeat turnover. 

I have a few off market two and three flat properties on the north and northwest sides of Chicago that would be good options if you're hoping to repeat your family's process.

Many many and I repeat many times when sellers say it is all cosmetic but a pro inspection will reveal problems.

Sounds like you have a positive experience, but I realize it would be hard to repeat.

But once I use up my cash reserves, if I don't learn how to use OPM, I don't want to wait for a few months/years to accumulate enough capital to repeat the process.

So you move and repeat. 

There is not room left to repeat typically and it is pretty much a done deal for smart investors from that point.  

You can repeat this until you decide the cash flow is what you want.