As far a the sprocket in the front goes, i think they make them as small as 22 tooth, and in the back, it is called a freewheel or a driver. Freewheels are generally larger and drivers are smaller. Drivers can go as small as 8 teeth i beleave.
Guessing an 11T cog (sproket), maybe a custom 10T.
It will if you have bmx (or bmx style) cranks.
the smallest sprocket is the highest gear.
It's 1/8" width, but the length is determined by the size of the bike frame, and the size of the sprocket/chainwheel you're using.
i would assume you have cranks with a built in sprocket, if this is the case, you can't
Not a sprocket only, but you can buy a 23-tooth freewheel that should fit.
the easiest way is to go to your local bike shop
change out the hub
There are two different hub designs for BMX, freewheels and freehubs. You need to know what you have if you want to replace the sprocket by the rear wheel.
It depends on whether you are talking about the front sprocket (the one at the pedals, called a chainring) or the sprocket at the rear derailleur. The lowest gear at the front is the smallest sprocket/chainring. The lowest gear at the rear is the largest sprocket. So if you combine the smallest sprocket at the front with the largest sprocket in the rear you have the lowest gear available on your bike.
You might have to either lengthen or shorten the chain, depending on if you're getting a bigger or smaller sprocket.
Of course it will, but in my opinion freewheels arent the best