At an appropriate point re-fi a package into a commercial loan which will achieve your lowest cost of funds. 

There are a myriad of ways to set that up to achieve your - and your investor's goals. 

What’s the single greatest thing that helped you achieve this?

Really, I think you should consider how you'll learn best and which route helps you to achieve your goals and go that direction.Regardless of where you learn, you'll need to get educated and work hard, and you'll need to have a support team around you, so learn, network, and grow into a real estate investor.

What is the reasonable rate that capital can be deployed into a major market and achieve 20-30% rates of return on cash?

The power of setting intentions is real and setting small simple goals (habits) help to structure the path to achieving much bigger goals.  

Work extra jobs if needed to achieve the savings goals you have for yourself while your living expenses are low.

The power of setting intentions is real and setting small simple goals (habits) help to structure the path to achieving much bigger goals.

It's all fixed up and you should attract higher quality tenants that want to stay longer becauseits in a good neighborhood.If you buy\hold a home that needs repairs and isnt as nice, you should be paying less upfront but you want to adjust your budgeting higher because you are choosing to repair over time, you won't achieve top market rents, and you might have higher vacancy because there is a nicer house down the street than yours.You can choose a good neighborhood to begin with in order to mitigate vacancy.

That is a sophisticated value add.Appreciation is more passive than value adds, but also takes much longer to achieve large gains.If you simply buy an RE (SFR to quad) off the MLS that has no value add, you will be waiting on rent appreciation to generate cash flow.