There's no set answer to that, it depends on what your preferences are. If you want a bike that's easier to get moving - get a lower gearing(bigger sprocket). If you want a higher top speed - get asmaller sprocket.
That depends on what you are using it for. Obviously, if you are dirt biking, you should use a dirt bike, and otherwise use a street bike. Start out with what you are going to use the most - dirt (freestyle) or street racing.
freestyle, dirt, street
That would depend entirely on how you use your bike (motocross or woods). If you race it, what do you want it to do ... overall top speed, pull holeshots, etc. By the way stock gearing on the 98 is 13/51.
Not really. It won't have the gearing and it won't let you get aerodynamic enough. Odds are you wouldn't even finish the race, let alone be competitive.
You should use Baby Luigi and the Quacker bike. Trust me it work's. That's how I unlocked everything!
inch
It depends on the gearing of your vehicle. I would use the second gear in my car.
You should use 93 Octane in your bike.
whene you are rideing at night
skiers use jumps (also called kickers or launches) or rails to do Freestyle skiing
You should use daisy and mach bike
There are several different options in order to see some example of freestyle videos online. The best choice would be for sure to use the search string "freestyle" on YouTube. Besides that also other video sites like "ClipFish" or "Vimeo" should be checked.