Development of CUPS Filter

I want to write an print job interceptor which allows me to hold / accept print 
jobs after they have been submitted. I thought it would be a good idea to 
implement a filter which would initiate a popup window prompting me to accept / 
decline the print jobs. I also would like to provide some information of the 
print job in the popup windows.

Is this possible with a CUPS filter and is this the recommended approach.

I though it would be best to modify the PPD file used by the printer to include 
the filter as it would ensure the filter is used for all print jobs. Is this 
asumption correct ?

Where do I get the page count from for the job ?