Hi Mario -
I started purchasing rentals before I bought my own house for cash flow. I may not have done as well as some of the folks on BP but I'm up to three now, which took be six years.
If I could go back to considering my first, I'd say if you have friends/family that have enough $ and you are confident in your ability to BRRRR (buy, rehab, rent, refinance, repeat) then you do not need to worry about fronting the cash yourself (except maybe a portion to show you have skin in the game). If you DON'T have investors or another source of money (hard money is an option but higher risk, harder to get, and more expensive) then buying something w/ 20% down may be your only option.
That being said, putting down the 20% on what has to be turnkey (since you don't have more $ to rehab) is a VERY slow way to grow a portfolio and the cash flow you get will take a while to build up. But hey, that's what I've done, it builds credibility, and six years later I'm looking for my first investors to accelerate growth.
Best of luck!