Outsourcing VS building an in-house property management team??

[Wilson Smith]

One of my preferred phrases is "Let Painters, paint." Guided by this principle, I delegate most tasks to skilled professionals to ensure efficiency. I currently outsource to a full service property manager who excels at their job. However, their services come at a high price—10% of the gross monthly rent and an additional 100% of one month's rent as a leasing fee. Considering that my properties generate an average gross rent of $1800 per month, the combined leasing and management fees amount to approximately $330 out of the 1800$ a month rent. 

With 30 properties, this results in an average of 2.5 new leases each month, costing $4500 in leasing fees and $5400 in management fees. The $10,000 a month price tag has me considering hiring an in-house property manager for around $4,000 to $5,000 per month. As my portfolio expands, I can gradually increase their salary, albeit at a slower pace than what it would cost to outsource the property management. My question is, when should I switch from outsourcing to employing an in-house property manager?