Depends on the diameters of the bars. Usually, but not always, they're the same and can use the same grips.
It´s the Stem, it holds the bars and match with the frame with the help of a headset.
Depends what size you are im 5 feet 10 and i ride a 20 inch bmx bike
depends the age and size
BMX bikes pretty much all have 20"wheels, which makes all frames very similar in size. On top of that BMX is almost entirely ridden standing up, so bike size doesn't matter as much as it does for road riding for instance.
BMX bike ramps are usually made out of material such as chrome or aluminum. They have to be durable enough for multiple people to use them at the same time.
you can find a BMX bike in halfords
The bmx thruster rampage bike is a exellent bike
One can buy a custom BMX bike in Las Vegas from a few stores. One can get a BMX custom made from 'Just BMX', 'Bolder BMX', 'Bike World' and 'Vegas Bike Store'.
BB usually stands for Bottom Bracket, the part which holds the cranks/pedals to the bike
It depends on the length of the chainstays on your frame.
Sure. You need to make sure that the stem match up to both the fork and the bars though. Depending on what bike you start with you might have issues getting brake levers and shifters to fit.