[Sam Grant]

MAF, chipset, wastegate (my favorite mod), cat bypass pipe, maybe an exhaust will get you about 65-75 more rwhp from stock. (Comes from freeing up the intake and the added boost most chipsets are programmed for.)
Throw a turbo and piggyback fuel controller on or get a vitesse kit like mentioned and the skys the limit. Injectors are needed once a new turbo is in and If you are going to do it all at once its way easier just to kit a Vitesse kit then buying everything separately. (These kits dont come with injectors or a wastegate though)

Also once you do all this stuff a wideband is kind of needed - all depends on what you want.