Lower weight wheels can have a benefit on fuel economy - especially if they are not larger and the same tire (compound, diameter, width, and pressure) are used. There are theoretical exceptions to that, but they would require a small difference in mass and that the mass be inordinately confined to the outer portion of the wheel.
Any changes in fuel economy will also be positively correlated to the percentage of your driving that is "city" or "stop-and-go" as the torque used to accelerate the wheel is the reason mass and mass distribution influence economy; at constant speed, the change in mass or distribution of mass is theoretically irrelevant. Don't expect a large change, though some may have seen large changes.
Sorry I can't help you with the tire choice, but a search probably could.