My opinion......
To start off. I would go ahead and get a race buggy to build, it helps, and don't get an all out race engine or a cheap one either. For example,
a Mugen, Associated, or losi or whatever buggy you choose is around 5-600 bucks...
Add an engine that you can learn to drive easier like a Nova .21Bf 3 port 150 bucks.
If you just want a super engine, get one for when your ready. It never hurts to romp on a 3 port and keep the sweet engine in good shape.....
7955 Hitech servo for steering and a fast lower priced servo for throttle
Dynamite 053 pipe 50 bucks
Airtronics mx-3x radio 200 bucks
You don't have to buy the most expensive stuff, but do get a good race buggy.....and a proven engine like Nova, werks...etc....If you really like OS then get the Ninja or wait for the new OS coming out soon I think.....