How will remapping affect my fuel consumption?

Depending on what your requirements are and your driving style depends on what your fuel economy will be. If you go for an outright maximum power output and drive it as so, you can expect to see it decrease as it would without the map. If you get the map to increase torque low down and drive conservatively then it is likely that fuel economy will increase. Please note that fuel economy gains are only likely on turbo diesel engines, petrol engines generally stay the same with some reporting slight improvements, never a loss.