Application development

I have been in discussions with ERSI about developing an application that did calculations on parcels. (An example would be, a particular zoning of a parcel in my city is SF5000 (that means that a parcel has to be at least 5000 sqft to be legal), it also means that a 10,000 sqft parcel can be divided into two parcels). I would like the application to pull the data from the city Assessor and identify all the parcels in the city that may be at least 10,000 sqft or larger. A second thing it would have to do is the average calculations for multiple parcels. One problem is that ArcGIS Desktop is not able to directly incorporate a service that is hosting a parcel dataset (The city Assessors office has the data and we have no problem accessing it). The 3 questions I have for you are: 1. Are you able to create an application that can do the calculations? 2. Are you able to grab the data from the assessors site and incorporate it into the application? 3. Would there be a better way of doing this, such as building an application to do all of that and cross-referencing it against the City’s own GIS site. I attempted to design 3 exhibits (labeled at the bottom) to help explain what I’m looking for the application to do. Thank You.