Changing the motor wont be took difficult, get an SHS/Rocket 16TPA neo (Which is more of a balanced motor) and that should help it feel more snappy. Consider using a 9.9V LIFe Battery as well, that will really help it along too.
As it's your only rifle, I wouldn't take a gearbox apart as of yet.
Most AUGs come with plastic hop units and they are perfectly fine and very easy to access and take apart. Just change the hop rubber to a Guarder Clear or Prometheus Purple, clean the barrel and you'll be fine.
Getting a replacement outer barrel assembly is quite difficult. I would suggest just using it with the current setup, even the long barrelled AUGs are still quite short rifles.