6-8 is about the norm for your stock internals granted that they are in good condition, which the compression test would show you.

As far as not installing the turbo until you have stuff done goes.. the thing that u need to be sure of before you install the turbo is that your fuel system is up to par. You are going to have ot have a way to increase the amount of fuel that you are dumping upon boost. Either an FMU (which is the rigged & not so great way to do this.) or Chip your ECU with a nice fuel map in there. I suggest getting your ECU chipped & have someone with a similar setup burn you their settings so that u can use it as a basemap to start from.

Best of luck to ya