Real Estate Leverage

[Guka Kagu]

I'm so confused. I watched so many you tube videos but still I haven't gotten the answer.  Is there any specific book that would answer the following questions?

1. How does investors use leverage to buy rental properties? I always hear people saying mortgage debt is good. Don't use your own money. How? Homes are so expensive plus interest rate is so high. Rent isn't that much. 

2. Investors/wealthy people don't take out salary. They take out loan. How does that work? Let's say their business is $1 million, they take out $100,000 loan (income), what do they do the next year?

Let's say you have $500,000. Which one is the best option and why?

1.Buy 1 property for $400,000 cash (no mortgage, positive cash flow after expenses)

2. Buy 2 properties 400k each with 225k down for each property (interest rates are so high - it will eat up all the rent). 

3. Buy $950,000 home, pay $450,000 cash, $450,000 mortgage. LTR will cover the mortgage and other expenses. STR might be profitable.