I'm looking at purchasing a stage 1 ppc for my 2.3lpt 9-5. If I later decide to upgrade to stage 2 or 3, do I have to purchase another ppc or can the software for stage 2 and 3 be loaded onto the one I purchases for stage 1?

Stage 1 & 2 software is the same. As long as there is a stage 3 PPC available for your car you will be able to upgrade the software at a discounted price should you wish to do so.