fuelc economy will almost certainly enhance once u cross the 5000km mark.my idsi used to give 11km/ltr in local driving when it was below 5000.and after that, it hardly ever dropped below 14km/ltr.as for the first oil change.i wud recommend u to get it done at 3000kms. always get it done at 3000.5000 is fine but hurts the car in long run.