Just my experience on this, but the only time a contractor should ever partner up is if they need the financing; if they want a piece of the pie they had better bring more to the table than leads and some existing clients.
Every estimator I hire has existing clients and leads, and can even estimate to some degree. For this I pay a fair wage, and they don't get a cut of the business. Sure some salesmen want a commission but estimators don’t typically get one.
"We are trying to create a mutually benifitual relationship.
Yeah me too, I have a mutually beneficial relationship with everyone that works for me. When its stops being so mutual, they either quit or I fire them.
Let me tell you something about estimators and salesmen, they are not as important as they like to tell everyone. Sure your estimates need to be good guesses, and if you don’t sell work you wont do work, but it's your PMs that will make or break you.
You can take the best estimate in the world and poorly manage the job to the point you lose money, or you can take a stinker of and estimate and aggressively manage it out of the hole. Sure even best PM cant save a bomb estimate but they can manage the loss.
Estimators are a dime a dozen, it’s the good Project Managers and Foremen that are hard to find. It also sounds like this salesman buddy of yours sold you on something.