I'm a little confused, what am I actually supposed to download to play this game?
Go here
You must be registered to see the links
I recommend selecting the Full Pack Torrent option (much easier than the split file options via Google or Mega) but then only initially selecting to download the main game (approx 60 Gb). Get that up and running then come back later for the Optional Mods (a further 150 Gb).
It will take a long time to download (I leave it running overnight) but it's simple to set up from there as no need to join files.
There are more detailed instructions in this thread. Just search for TurboJoe and he's probably written better responses to this over a hundred times.
Best of luck and see you on the other side. And, yes, it's worth it