I'm about to buy a GTS-4 soon. I know it has turbo and AWD, but I was wondering if it is possible to modify it to have 2 turbos? Can the engine handle it? And would it even be worth it? Any advice would be greatly appreciated.

you can but why? The turbos you would have to run would have to be quite small and I see no improvements you can possibly make. The factory R32 RB20DET manifold is a T3 flange which means you can stick some pretty a good size turbo on it already and remain low mounted.