I completely disagree with the lucky stage 1,2 and 3 - fine gear, but so far from essential up grade it's not true.
Trigger's are personal - for me (and I've had them all) I would suggest the VP Scythe trigger si the best bet, but it's a very personal thing.
I wouldn't want to downgrade from the stock reg as Mikey says
My thoughts...
1) Rail & Purging On/Off - £25 2nd hand. Will make the biggest difference to shooting with correct posture.
2) Feedneck - qlok = £27 on paintball warehouse if memory serves. Not from the point of view of convenience, but lowering profile - the stock one is too high
3) Halo or reloader B - The rate you feed the hopper will make FAR more difference to your ROF than anything else. The weight thing isn't what you think - a full egg weighs the same as a full halo, and the reliability issues with Reloaders etc have by and large been sorted. You may also want to bear in mind the saying, "You can't make a tourney without breaking some eggs..."
4) Trigger - it's a very personal thing, but most people hate the stock one. Several good ones around.
Controversy still rages about QEVs - up to you. New barrel when you can be arsed - the stock one is not a thing of beauty but will serve fine for a while - if you can't hit them, get closer
Then get to work on the cosmetic bling factor