Ralph,
Irrigation zones divide your lawn and garden areas based on several different factors. Sun/shade conditions, soil type, water pressure and flow rates, plant material. One extra zone will not cause additional problems down the road. It's like saying you would only want a four speed car and not a five speed because it will give you more problems down the road.
Deal with the contractor that you feel the bestworking with. Don't hold your breath with the pro coming down in price. If he's any good, he's probably pretty booked this time of year, and has other jobs if you don't want the installation slot.
Mick
Irrigation Contractor
Certified Backflow Assembly Tester