How to build your own track bike
So, you think you may be spending lots of time at the track, either doing track days or racing. It only makes sense to have a dedicated track bike, if only so you don't have to worry about crashing your daily ride. Here's a general list of things you will need. Keep in mind that all tracks have slightly different requirements. Also, if you're going to be racing, you'll have to follow the guidelines published by the sanctioning body for your event(s). So, read up. This will get you started.
See also: Reducing weight on a track bike
(Looks don't matter; function does)
To Do List
Inspect and Repair/Replace/Adjust as needed
Minimal Bike Spares list
(optional *) items aren't really required, fractionally enhance bike performance, are too expensive, time consuming, or are not absolutely required for track days.
NOTE: Be aware that plenty of EX250 race bikes are sold each year, usually from October through March. You will likely get a better, cheaper, completely set up bike buying one of these than doing all this on your own. But then, what fun would that be?
For another look: Here's a site that recommends parts and mods for a race bike. Good links, too.