Congrats on the new GS. The TPMS sensors itself will cost you about $800, I would ask the owner if he or she still have them. Rattles and creaks usually come from the dash board, it get worst when its cold out. Most Lexus dealer became experts at fixing dash rattles, but usually the rattles will come back sooner or later after the fix. The small black box on the windshield is the rain sensor, I dont believe the 06 have the sat. radio shark fin antenna in the back. You can still get Sat radio, you just need to install a Sat radio module and a antenna. The engine ticking noise is pretty common in the Toyota V6, the GS350 has a even louder noise due to the direct injectors.