For example, mixing in flips, focus on the BRRRR method, targeting larger buildings, etc.Similarly, what would you deem the next step forward for someone who has focused solely on buy and hold single families? 

I love the BRRRR method and it works well.  

However some of these Roth IRA and 529 are after tax money but you still get the benefit while withdrawing tax free.

Based on my last 2 years doing wholesale to build cash to buy rentals it is not my preferred method and I don't recommend it if you don't need it to build cash in Houston without putting in tons of work and hours.  

There are a lot of ways to buy houses with little money down.These are the methods that worked best for me:Method 1: Find a Lease Option Tenant who has down payment $$ before you close.This is how I bought my first investment house:I have a local bank that only requires 15% down, so I found a tenant who had 8% (of my purchase price) in cash and a car w/out a loan.

There are a number of methods to reattach loose corner bead, but you MIGHT need to replace it, but that's not a big deal. 

You can also arrange, with Low and No Money Down methods, to Buy a Rental that you would live in and just move from one Tax-Free Residential Sale to the next one, for the rest of your life.

(Reminds me of some RE investors, LOL)His system to teach was the "Think Method" if you think you can, then you can!

For rentals, that is a long-term investment and you would not be able to get the money out again in a short period of time (the fastest way may be the BRRR method).

If you're new to this, I highly recommend listening to as many podcasts as you can to learn about all the different methods people use to invest.