That makes it a little easier as you know the size lots that you will be working with. Go with the biggest deck that will fit on the properties and be the most productive.
Get your friend to let you demo the different units and see what works best.
Aeration for free!!! That is one of the best money makers so don't give it away. If you are planing to "PULL" , What are you using. If it is one of those $200.00 dollar trailer thinks you buy at lowes than sure give it as it does not do much anyway. If you are using a real aerator than you have to charge as it is rough on equipment and you have to pay for the machine.
Also if the lots have irrigation you will have a hard time mowing as you pull because you have to go around the heads. Good luck.
We give you leisure time.