This doesn't speak to investing in multifamily vs sfh, but I can share my experience/evolution in rei since starting this past summer. My sister and I co-owned a 14 unit which we inherited--there was a decent amount of deferred maintenance. Knowing this, but not really knowing anything about rei or how to obtain money for the necessary repairs, I wanted to sell, but my sister did not. So, she bought me out. I then bought a sfh rental with the proceeds, and said ok, now I've replaced that income. Shortly after that, I really got the real estate bug.
When you do the math and see what your monthly cash flow is with owning a property outright vs using leverage to expand your portfolio, there is reallly no comparison. The numbers just come out better when you use leverage to buy more properties. That being said, I don't go any higher than 25% loan to value, just to keep a safety net in place should a market correction be around the corner.
I've done a second cash out refi of a rental which used to be our primary home years ago. So, we've now done two cash out refis and I'm about to use this money to buy more property. If you're happy with your sfh, you might want to refi and take the proceeds to buy the multifamily. Just play with the numbers and see how things come out. Once I started doing this, I really saw that my portfolio and my monthly cash flow can increase MUCH faster than owning one property outright and using that to save up to buy more. Hope this helps in your decision.