How much should project managers get paid?

[Kendall Seals]

I am expanding my business and I am adding project managers to manage my flips. How do you fairly compensate them so that there are incentives for them to make as much profit on the flip without giving them all the profit? 

I’m leaning towards base pay+commission. How much is too much and how much isn’t enough? How do I keep them from leaving and doing there own thing? Would love to hear thoughts on this.