@Darth:
Well, we do know that he is probably a mathemathical genius.
That's highly possible. His fruit demands a lot of understanding. Other Devil fruits require understanding of Newtonian physics on intuitive level at best, Light Logia requires understanding of relativistic physics, and relativistic physics isn't very intuitive. Furthermore it requires a lot of precision and calculation. I think Kizaru needs to "program" himself for specific tasks and moves before he converts himself to light. Very demanding fruit is one of the reasons why I think Kizaru isn't as stupid. Other reason is the fact he follows the doctrine of "Ambiguous Justice" and that need a lot of negotiating and joggling with ideals of Absolute justice, actual moral and what can practically be done. It's no easy intellectual task at all.
–- Update From New Post Merge ---
@Darth:
Wait, I thought he took a ship because he would need some way to transport all the pirates he captured.
You know, 500 of them? I recall that Aokiji said he would need to kill Luffy because he didn't had a ship to transport him on. Maybe it's the same for Kizaru?
Also, I can't seem to recall Akainu giving soldiers suicidal orders…
But than why would he need to ride on cannon ball? He may have more than one reason to take a ship and transporting prisoners may have been one of them. But the Ship could just follow after he departed from HQ, after all there was enough marine to guard prisoners on Shabaody, after Kizaru would caught pirates, while waiting for the ship to arrive.
Akainu ordered soldier to go back to the Battle on Marineford. They were simple soldiers, they couldn't hope to accomplish anything in that battle, save for adding to victim count. And he were to kill them, have they not listen.