The same is true for a house—placing a tax-advantaged asset into a tax-advantaged investing account cancels the tax advantages (or many of the immediate ones).Maybe @Michael Plaks or @Kaaren Hall can explain this better or correct my understanding here?

Is that true ?

Once you understand LLC and irrecoverable trust would give you more harder time getting financing, then you start having second opinion, this is also true for what people hearing about this and that tax advantage in real estate and stuffs.

As for a lot of the "your returns will be better with more leverage" that is typically true if your unleveraged yield is higher than your cost of capital.  

The more complicated your business structure becomes, the more problems it can actually cause such as when looking for lending options, getting the best interest rate, keeping clean accounting, filing taxes, opening bank accounts, getting credit cards, executing a 1031, making title insurance claims or even triggering a due on sale clause, etc. 

this is old  tried and true method of simply having you pay them to get credit cards .. there is no need to pay for this service.. unless you want to of course.. there is no magic bullet ut there that is going to give you credit and financing unless you actually qualify for it.But zero interest credit cards are used by some to do rehab and then pay them off issue is though your fico score drops like a rock the second you take on all these CC.Also starting out there is zero chance of getting any kind of business line of Credit that is unsecured.

sounds like you are on the right track - house hacking or BRRRR to jumpstart the journey is a pretty solid tried and true gameplan

Estoppel letters are signed by each tenant and counter-signed by the owner as true and correct.

Since living here I’ve put in a new HVAC in both units and kitchen into one unit, I’ve max out my credit card, and have had my parents help me.

I personally like the credit card balance transfer check route, since it's interest-free for a decent amount of time (aside from an initial 3.00% fee).