Wa salam,
As per my knowledge donât go for gear oil change unless you feel any problem in the gearbox or shifting. The new oil will mess up with the gearbox.
For plugs your mechanic can tell it when he will open the plugs. Sometimes even after 5k they are needed to be replaced but sometimes they work more than 20k, depending on the carâs condition, the atmosphere and the driving habit. Better ask your routine mechanic to check The plugs
I think they will cost around 1k each.
The average reset thing is normal.