There are electrical codes for wiring outlets in kitchens. Older kitchens will not have this layout but during updates or remodeling, the current codes will take precedence over the old plan. Since you will need to have any electrical work inspected, be sure to check with your state codes. Also check to see whether a permit is necessary before you tackle any wiring projects.
The electric code requires that you install outlets on countertops every 4 feet and the height cannot exceed 18 inches. If you place the outlet 18 inches high, you will need to decrease the width between outlets. Any appliance with a 2-foot cord must be able to reach an outlet at any point on the counter. Also remember that you need to place outlets within 2 feet of the ends of the countertops when you plan the placement.
Wall outlets do not have a specific height according to electrical codes but a practical height is 18 inches off the floor. This is an easy reach for inserting plugs and out of the way of any floor cleaning liquids.
Microwave outlets are different from other outlets in the kitchen since they often attach to a cabinet and you string the wiring through the bottom of the cabinet. Again, there is no code as far as the height of the outlet from the base of the cabinet, but a 2-inch height moves the installation of the outlet away from the framework of the cabinet.
Appliances each need their own separate wiring circuit, and the placement depends on the length of cord for plugging. Typically, the same height as wall outlets is applicable for appliances such as refrigerators and stoves. However, if you don't want to have to bend so far down, you can place it higher for convenience.