1. Carth/Bastila told T3 to search for the Jedi, Sith, or Republic for help aganist the real threat. You get the hologram by having influence and a Intellegence of 14. T3 found Kreia and they rescued the Exile on the Harbringer...
2. Because the Ebon Hawk was at Malachor V. I suppose that they wanted its location of the Trayus Academy to remain secret, being that it was the place where Revan corrupted so many Jedi. The Ebon Hawk, Revan and T3 went there because Revan rememberd something horrible. When there, Revan gave the command for T3 to find help aganist the Sith Threat. T3 left Malachor V when Revan went off to fight aganist the threat.