Re: Gear range or Cassette size for shifter kit
Cassettes are used on newer high end bikes with the freewheel integrated to the hub. The sprocket "cassette" slide on to a spline. This system allows for a tiny top gear, 11t or 12t is possible.
What you probably have is a "cluster" or freewheel if its an old bike. It screws on the hub and the freewheel is built into the cluster not the wheel. 14t is usually the smallest gear possible. I have seen smaller but it is rare and used on old school racing bikes.
A 14 to 28 is the most common setup here. 14 to 32t or bigger will require a special rear derailleur. If you really have a cassette rear hub the you can have 12 to 30 or something like that.