We started in Jan 2017 and now have six SFR, all paid for in cash. Now, we did start with a bunch of savings since we were flip-flopping on investing for a while. We're great at saving, though. So the first year we bought two, then one each every year since. Last year's house is actually going to be ours when we move back to the US, but for now, we have it rented for six months, minimum.
It's been great because after we got some extra cash reserves in the CapX fund, we don't really stress when something breaks or a tenant doesn't pay. That didn't happen til late last year, the guy with a FT job, not affected by covid, has the lowest rent which hasn't been raised in three years...he has paid once in five months. But my PM deals with him and we might be able to recoup that money from the county. During these months I took the tax/insurance money from the "vacancy" account and went on. No mortgage to worry about.
So I really like the all-cash method. It's slow yes, and sometimes I do think maybe we'll finance if we can get a mortgage when we are in the States. Might make things go faster. But if we do, I can't see doing more than two at a time until the mortgages are paid off.