Great question, and I'll answer it from a different seat than most people in this thread. I'm a lender who's closed around 500 transactions over 10+ years, and I've watched investors on both sides of this decision. Some built real wealth. Some blew up. The difference was rarely how fast they bought.
My answer: Start with one, but structure it like you're going to buy ten.
Here's what I mean. The mistake isn't buying one property first. It's buying one property casually. First-timers buy in their own name, use a loan program with no thought to what it does to their DTI, dump all their capital into the down payment, and then discover 18 months later that they can't qualify for property #2 because property #1 was set up wrong.
If I were starting today with capital for one property, here's what I'd do:
Buy one, but underwrite it like an institution. Learn the fundamentals on a single asset: tenant screening, maintenance reserves, what "cash flow" actually looks like after CapEx (it's less than the spreadsheet says). Tuition on one property is cheap. Tuition on four is not.
Preserve borrowing capacity from day one. This is the part almost nobody thinks about. Your financing strategy IS your scaling strategy. Most W-2 investors don't even know DSCR loans exist, programs that qualify you on the property's rent instead of your personal income. Whether your first loan is conventional or DSCR should depend on your 5-year plan, not just today's rate. Talk to a lender who works with investors before you make an offer, not after.
Pick one market and one strategy and get boring with it. The investors I see succeed long-term aren't the ones chasing whatever's hot on YouTube. They picked a lane, say single-family rentals in one metro targeting 7-8% cash-on-cash, and repeated it until they could underwrite a deal in their sleep. Your second and third deals get dramatically easier when you're not relearning a new market each time.
The "buy multiple sooner" crowd isn't wrong that leverage and time in market matter. But speed is a second-property problem. Velocity comes from systems, and you build systems by doing rep #1 well.
Long-term portfolio advice in one sentence: leverage wisely, grow wealthy. Debt is the tool that builds real estate wealth, and it's also the thing that ends it when it's used impatiently.
Happy to answer financing questions if anyone's mapping out their first or next purchase.