we g18c upgrade questions

[oldun]

ive got a we g18c gen 3 on the way with a co2 mag which i will be ultimately modding more for target shooting/plinking than skirmishing.what parts should i be looking at upgrading to make it more robust/accurate? ive seen reference to non hop up barrels in relation (i think) to aipsc type guns what are their good points/bad points ,reasons for existence? ive built/modded a few airguns before now so have some technical awareness but new to the airsoft stuff.
if we could avoid "should have got a t.m, w.e suck!" type comments as ive taken these onboard allready that would be great