I wouldn't dive straight into stage 3. that is a big step for the serious modder.
I would personally need to uprate everything else before bolting on a big turbo.
really you should sort out the suspension and brakes before you start on with the maps. But the best way is to get a map first and you will be addicted to the buzz and the rest will just have to be done.
If you go Revo or Superchips then going the next stage doesn't cost to much if anything.