How often are soils tests done on these properties?
How do you know that there is a need to "fertilize" 3 times a year?
Is there a real good reason to aerate those soil once a year?
How high do your cut the grass on these lawns?
What happens to the grass clippings?
The commercial "lawn care" company that does our church lawn comes in 4 times a year to spray something around and the person in charge trys, very hard, to tell me that he can tell what that lawn needs just by looking at it. Every soil scientist I have talked with tells me that is immposible and even many horticulturists wil say that, but there are people that have not had any schooling in either soil science or horticulture that say they can.
Test the soil of each property, periodically, and "fertilize" according to that soil test.
Determine how much organic matter is in that soil, because adequate levels of OM in soil can eliminate the need to mechanically aerate the soil. Needing to aerate any soil annually indicates insufficient levels of organic matter in that soil.
Cutting that turf high can shade the soil enough to limit the number of weeds growing there.
This, on Natural Lawn Care, from Ohio State University may be of some help.

Here is a link that might be useful: Natural Lawn Care

The boss is going to be concerned with keeping those 42 customers you take care of. So, after you and the boss get educated on how to go green you will probably have to have a plan to educate some customers as well since some of them will expect or even demand the non-green way of doing things. Keeping customers makes a happy boss and a happy boss translates into a paid employee. Having a few well-documented demonstration properties where you have been successful with green methods might be the best way to bring the more stubborn customers around. Also, those demonstration properties will help you refine your system. Some properties may temporarily look worse when you take them off of the artificial stuff so a few success stories to point to might help the customers to remain patient during the transition. Some customers might want you to hold off for just a little bit. For instance, if it is one month before a customer is going to host his daughter's wedding in the yard, he will probably not want to try anything new until after that is done.