Personally if you are decided on the car just get it and bank the money for a little while. Break it in. Run the thing.
If you are going to a track -
Find out what kind of tires work best out there and get them. Tires are the first key to a track setup. Get the shocks and suspension setup after that. Learn the track and see what breaks on your particular car and spend the money on a few spare parts right away. Nothing sucks more than breaking and having to go home. Also on a track servos might be the first big thing after tires if the stock ones won't alow you to turn very good.
If you are bashing at home and don't get crazy you probably won't break many things. Drive the car for awhile and see what bugs you the most and spend money on upgrading that.
Some of these choices will turn out to be your own personal preference vs. what we try to tell you so the same advice holds - run it for awhile and you'll know what to buy next!