IndyYZ85 perhaps provided the best advice regarding a large pile of cash. As a warning, I purchased a 2002 CR250R in the summer of 2005. I'm a 30+ plus rider that hits the tracks with the kids during open practice. Therefore, I do not push the bike beyond its limit. As of yesterday I have over $6k in the bike. I really ejnoy riding the 2 cycle and plan to keep it considering the investment. However, in hind sight I should have purchased a new 4 stroke in the summer of 2005 instead.
To answer your question I would purchase a new air filter and make very sure that it is properly cleaned after every ride. Drain the coolant and replace with factory fluids. Change the oil in the lower end now and after every other ride. Check the coolant and the oil in the lower end frequently until you become comfortable with the bike. Check the brake fluid and the brake pads. Repair / replace them if necessary. Use your manual to guide suspension adjustments. Mix the fuel 32:1 unless otherwise guided in the manual. Replace the plug and buy several spares. One third of the extra plugs will be for you and others will be for those at the track who foul and did not plan ahead. Check the air in the tires, they should have 12 psi or more. Anything less then 12 psi and you will risk pincning the tube. Make sure the spokes are tight. Insure that the chain has the proper sag. Clean the chain and apply chain lube. Make sure the bike is not leaking fluids. Also, when you change the oil in the lower end, make sure you do not have an air bubble. This can be prevented by measuring the fluid in connection with the mannual.
If you have the time and patience, then tear it down to the frame as previously recomended. Otherwise ride it, do not skip recommended maintenance and repair / adjust as necessary.