You can't unlist a car. Once a car is enlisted, it stays enlisted. I believe it used to be possible, but isn't anymore. Perhaps that will be added again later.
I don't know of any way to get specific numbers for your cars stats, if that is what you are asking.
1. You can delist a car once you have enlisted it. If you do decide to delist any of your race cars you will lose all the upgrades you purchased for that car. You will not get any points back.
2. you can find a lot of car info at tcbasic.com, or follow this link: http://tcbasic.com/raceway/ The info here isn't perfect, but it will be pretty helpful.
You can't delist a car. I have one I enlisted from when I first stared, never did any upgrades, and have no use for. But I can't delist it. At one time, I believe you could, but that feature has gone away.
Braking distance is how far fast the car can stop from top speed. The shorter the braking distance, the faster you get get through corners and such, since you don't have to start braking as early.
There isn't anything to say that a car which has never raced can't win. You don't suddenly start getting wins purely from "This car has raced X times". It's based on the cars stats, modified by it's upgrades and the driver skill. It depends on the other cars and drivers in the race. And there is some randomness involved every time you race.