appx 30 units per full time handyman..

there is no fix formula, its more correlated to your net cash flow. 

base on my past experiences, 20 units can be near hands free, meaning your cash flow can afford to hire out, instead of doing all yourself.

right now, I have 3 handymans on 1099, we can fix 98% of all  problems, but if it related to structure, or major mechanical problems, I have to use outside help.