Usually, and depending on the microscope manufacturer, when a microscope is purchased software is included or can be purchased allowing an individual to take cell measurements. The Zeiss microscope that I use has this software included in the software package.
True, but this needs to be calibrated before it can be used - basically so that a certain number of pixels is equivalent to a um at a certain magnification.
The manufacturer's of the microscope should be able to supply an eyepiece micrometer. Stage micrometers - microscopeworld.com has some, and i am sure that are others out there, but they were the first on a google.