First off, you probably should have posted this in the Farkles section, but no big deal, maybe a mod will move it for you.
It will require quite a bit of fabrication and patience to end up with a nice looking cafe racer ... You can find some seats on ebay that have the cafe racer look, and you'll have to remove the factory rear tail section and figure out a way to weld up/ modify the stock rear section of the frame to fit the seat that you want.
You'll also have to do even more modifications if you want a different gas tank, which many cafe racer builds seem to have.
As for the headlight, you can use 36mm fork brackets from ebay to mount up a 7" (pretty common) or whatever size round headlight you want to put up front.
Then there is the exhaust, which from what I have been reading and what people have told me, is best left alone, as well as the intake... If you insist though, I recommend some Emgo mufflers to mount to the stock headers and of course a rejet.
You can find bikini fairings on ebay as well ( mounts around the headlight) that fit on the bike, if you want one of course. Emgo makes several different kinds of these for 7" headlights that are universal.
Here is several posts I found for you, relating to cafe racer builds for the ninja 250.
https://www.ninjette.org/forums/showthread.php?t=316365
https://bikebrewers.com/kawasaki-nin...racer-mr-ride/
Here is also some pictures for some ideas.