The most simple formula I know to build wealth is through real estate. In the United States real estate has doubled on average every ten years. If you buy one house every year for five years with a 30 year fixed mortgage, in 30 years your tenants will have paid off the properties and you should be worth one million dollars. 
Hello, yes if you leverage and then the house is in long term bull trend , you could easily become millionaire if you buy one every 5 years. However bear in mind that 1) the house price dont always go up
2)the interest rate may spike to a level even interest is hard to afford
3)house is fairly illiquid asset that you may not be able to sell after 30 years.
You are right. It is important to buy your home's in an area where people want to live.
Yes location location location
This requires much more than you think. You need Property Management unless you're a handyman and have clones of yourself you can do major repairs at the same time with. You need a "power team" which is comprised of a legal representative, contacts for the renters, and so on. All of those things require time from you, so good luck working a job at the same time unless you outsource. Then your personal cash flow from the properties will be severely impacted.
It can be simplified much more than you think. One property management company can provide all of those services to you and you can write their expense off on your taxes. I recommend buying new construction when possible so you don't have as many repairs initially.