Since I made the mod, I will explain. I only tested it with the English version, so I'm not sure if it works correctly with the German one. Apparently, someone has the exact same problem on Holowan Labs: http://www.lucasforums.com/showthread.php?t=154662 .
The order is supposed to be as follows:
1. In the Sith Academy, pick the datapad from the dead Twi'lek (who is actually Lonna Vash's Padawan, Kaah Ohtok).
2. Insert it into the console.
3. Open the Academy door from the console. It isn't necessary to play the holorecord.
4. After leaving the Academy, enter the cave. While you're crossing the bridge, several Sith Assassins will spawn around you. One of them, with a lightsaber, will drop a datapad, from which you can read that the lightsaber actually belonged to Vash. If you have the USM installed, he will drop the lightsaber as well.
5. Make your way through the tomb, as usual. Unlike the original game, you can enter it regardless of your alignment.
6. After you defeat Revan, you will see a vision of Vash lying on the floor.
7. Exit the cave, as usual. When you open the door, you, instead of exiting the cave, will go to the room where Vash is. She will awaken, and you will have a conversation with her. She will die regardless of what you say (although you can choose how) and you will exit the cave, with the Vash quest completed and your business on Korriban done.
The G-Wing was originally supposed to have a purpose: I planned to make a version 2.0 of this mod, with Sion leaving you for dead and going to Nihilus' ship. Then there would be the "Sion vs Nihilus" cutscene that was cut from the game and restored by Darkwarrior from the TSLRP forums. However, I had problems doing the cutscene with Sion throwing his saber at the player (it disappeared after returning to his hand, for some reason), so I eventually gave up.