Easy way: save 3.5% of down payment, buy a duplex or triplex. Live in one year, rent other units out. Refinance into conventional loan. Buy another duplex with 3.5%, repeat.
Hard way: save enough cash to buy duplex outright. Repeat.
Easy is a relative term. If this were easy everyone would be doing it, though it seems that everyone IS trying to do it right now. Your goal is pie-in-the-sky, too nebulous. Why do you want to have a stack of rental properties? I'm guessing someone told you that if you get a stack you can quit your job.