Ok, so I got from GOG FREESPACE 2 and DESCENT: FREESPACE BATTLE PACK.
How would you guys recommend on proceeding? Play the game vanilla? Mod it first? If so, which mod?
Yeah, get fsopen:
http://www.fsoinstaller.com/
Just download the installer and execute it, it will walk you through everything.
From the installer, you can also select mods. I would suggest getting FSPort, since it will enable you to play Freespace 1's campaign in the fsopen Freespace 2 engine.
To launch the game, get wxlauncher here:
https://github.com/wxLauncher/wxlauncher/
I'd play through FSPort first (the original Freespace Campaign). The story is way better than part two, and you will lose a lot of background if you play FS2 without having played through FS1.