PokerTracker

Since I will no longer be using PT2 and a new database will be created for PT3, is it safe to just install ALL of my postgreSQL versions (to clean up space, etc) and just start fresh with v8.3?. Are the older versions required for anything else?

The older versions are not needed, but please be absolutely sure you don't want to use PT2 again. There is no need to uninstall the old version of postgres, though I guess it will make the install easier.
PLEASE make sure you have a good back up of ALL your hand history files at least before you do this! And preferably do a backup of your postgres databases from within PT2 as well.

Over the past few months I had been making the switch from LHE to NLHE. I had been just getting comfortable with the changes and figured I would start fresh when PT3 was ready. I have no database I need to keep. I will begin new. Therefore, I figured I would clean up the computer a bit and rid it of old versions if possible. Just wanted to make sure lower versions were not required to be there.

Hijacking this thread, I wanted to ask if PT2 does work with 8.3 at all?
I couldnt get PT3 to work with 8.2 so I uninstalled it and installed 8.3 instead, now I get weird error messages in PT2 and nothing, absolutetly nothing is working anymore. Help would be very much appreciated, I need to access my PT2 database once more..

You'd be better asking PT2 questions in the PT2 forums, but you can start here:
It is possible to use PT2 with postgres 8.3