A terabyte is trivial amount of raster data, but it's a lot of vector data.
ST_GEOMETRY has improved over the years -- There have been ten minor
releases since 9.3.1 SP2 (twelve since 9.3.1), but you don't have access
to any of them.
You're looking at using retired software for a significant change to your database.
I would not recommend this.
To answer your questions:
2) No way to even provide a glimmer (all dependent on missing information)
3) Tons of concerns
5) Why are you hoping that?