Congrats! It's a great bike, both for beginners and experienced riders.
First, don't believe anything a PO tells you. Nobody likes to clean carbs, which is why hardly anyone seems to do it.
While waiting for your license, you should check all the obvious stuff, like tires, brakes, oil, chain, clutch cable, brake lines, coolant, air filter, steering head bearings, etc. This is also a great time to learn more about your bike by adjusting the valves (if the engine is too quiet, it's probably time to adjust), installing new plugs, changing the oil and coolant, and changing the brake fluid.
Get a service manual (they're available online, and check out the Ninja 250 wiki at http://faq.ninja250.org/wiki/Main_Page
. You'll see that maintenance and adjustments are very easy and satisfying with the pregen 250.
You'll have a much better sense of the machine, and a lot of self-satisfaction, and a thicker wallet, if you do all this stuff yourself. By the time you first throw a leg over it, you'll know it inside and out.
Good luck, and enjoy the MSF class and your new ride!