I am a big fan of having cash reserves for when Murphy hits...and sometimes he may hit hard. I have two quadplexes that I bought just under two years ago. My experience with the first is that I had to replace appliances & HVAC units in 3 out of the four units that where not expected. My cash reserves & available financing is what saved me. Another added bonus is that the property was a cash purchase, no debt service. Spring was around the corner & I had all units leased up within a couple of months.
My other quadplex required replacing only 1 HVAC & 1 stove , that was expected. The other HVAC'S are old but kicking strong. I do know that they can go at anytime and having reserves will help handle this situation. ... and as far as vacancies/turnovers I did experience that as well. 25% to as high as 50%.... so depending solely on TIMELY rental income is not always your best option to maintain operating expenses. As of this writing I am happy to say I am at 100% occupancy!!!!!!!
Wishing you continued success