Excellent, another convert.
The numero uno thing to get right on a TT bike is your position. You should be aiming to get your torso as horizontal as possible and be able to stay in that position through corners and on fast downhills. Having to come off the tri-bars puts you more upright, increases frontal area and causes more drag from your arms being in the wind.
Secondary to that is getting a decent set of aero wheels (50mm deep or more), then probably a pointy hat and skinsuit. Aero frame and forks is pretty well down the list, as are top notch lightweight components.