yes... if you have the right bottom bracket... it has to fit the cranks as in 19 20 21 or 22mm most likely......... and it has to be the right size for the frame.. if its bmx it will probably be US size or euro, spanish or standard. if you find the right bottom bracket with the right size bearings then yes..
A crank (or a crankset) is the thing that sits in the middle of the bicycle, has the chain on it and have the pedals attached to it.
No, only the one that was made for it.
Yes you can, but take it to a bike shop or someone who knows what they are doing
you can find a BMX bike in halfords
It depends if you have a 3 piece crank, spokes, brakes.
By crank do you mean sproket? The smallest iv seen is a 22t but there may be smaller, or do you mean 3pc cranks?
Bmx's don't come in sizes. They are all one size.
what ever size fits them for their intended uses.
The only thing on a BMX regularly called a spindle would be the crank axle. Although I suppose one could use spindle for the pedals and the wheel axles as well.
Usually not. It'll be fast at the start, but a small crank will limit top speed unless you can turn the pedals really fast.
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. I agree, but get at least a 20.5" frame.