From the angle you've supplied I think your position looks excellent. You have a flat back, and a narrow frontal profile (from what I can tell). It would be good to have a shot directly from the side at full leg extension, and also one directly from the front.
The helmet will be the biggest savings. From this photo it appears (although, again, difficult to tell) that you are dipping your head slightly. It will be important with the TT helmet to keep your head up as much as possible. Also, you should look into getting some lycra shoe covers. Your elbows (again, from what I can tell) appear to be quite a bit in front of your shoulders. Is there a way to position your seat slightly more forward, or the aerobars back a bit? With your foot position (as waterrockets mentioned), is it natural for you to "toe" the pedal like that? Or do you have your seat jacked up a bit high? Some guys believe that bringing their seat up will flatten out their back, but this is not the case. Are you wearing a skin suit? The fabric over your mid section appears slightly wrinkled; i believe you could actually go with a tighter garment on top -- skinsuit or no. Finally, is the number on your back sprayed on tight? If it's pinned on, and if you are permitted to pin it in this position, I recommend pinning it over your bum; where you have it currently (unless it is sprayed on) it will act like a parachute.
Those are just my thoughts; I will say that you already seem to have an excellent position and I think from here it's a matter of making micro-adjustments. As for your questions, there is a lot of controversy over where you get the biggest time savings. I think most would agree (after dialing in your position) that the helmet is the biggest savings, followed by the wheels. Over such a short time trial, I wouldn't expect more than 30 to 45 seconds total from equipment changes. Position changes matter a lot more. And, of course, training! As for split times, I try to pace myself as waterrockets has suggested. I try to get faster. Don't head out and blow after a few laps. Think of it like a carpet being rolled out: you get faster the further you go and by the end you really snap out the finish. You shouldn't be sprinting, mind; you shouldn't have enough left to sprint.
I'm sure other guys like DrConnell and Vinokurtov will have some better suggestions. I am eager to see what they have to say.