How many units is too many for one person?

[Joseph Baron Fuller]

I want to know what most property managers have in place to handle large amounts of units. I currently run 150 lower end SFR's, 5 Complexes less than 15 units per and a mobile home park totaling 230 units in two cities with myself, another worker and a maintenance guy, This is done for another person, I'm consistently on the phone from the moment I get into the office in the morning until when I get out clocking 200+ phone calls a day on some days and with general office work, and a pest control company run out of the same location taking an hour to two out of my day. Given the same structure and amount of units, what kind of staff would you have? I'm deeply overwhelmed sometimes by the job and want to see if it's so difficult because of past mismanagement and disorganization or because we don't have enough staff. Feel free to share your personal setups and make me feel like a wimp if necessary, I'm really looking to see the capacity of a well run property management company on average. Thank You.