Staged performance packages are SALES packages for specific companies. Company A's Stage 2 is Company B's Stage 3, so there is no such thing as a universal truth when it comes to Stages. Stages were designed as a sales package so someone does one stop shopping and they get a discount. Kind of like a #4 at McDonalds...everything for lunch + you save 30 cents.
GENERALLY SPEAKING, here is what the various stages are:
Stage 0 = engine management alone
Stage 1 = engine management alone
Stage 2 = turboback exhaust + engine management
Stage 2+ = stage 2 + a few other bolt ons
Stage 4 = small bolt on turbo + fueling + turboback exhaust + engine management
Stage 5 = anything above stage 4
While these are generalizations, DO NOT fall into the trap of labeling your car as a "Stage X" and expect people to magically know what you are talking about. Post specifics such as "I have a Cobb Stage 2" or "I have a TurboXS Stage 4", or better yet...forget stages and post 100% of your mods.
And for purchasing, stages are fine and dandy and easy. But, a careful shopper can get the same performance by buying used or piecemeal vs. buying from a staged package. Just decide which is more valuable to you...time spend bargain hunting or the ease of a staged package.