So I want to be able to do the following:

1. Click on a map to create a point.
2. Then using  my tracts file that has my data I want it to start to systematically start selecting traces based on the following:
   1. Start with the closest tract.
   2. Then select tracts one by one (always going to the next non selected tract) summing up the [market share] column until Marketshare is > 70%
   3. Make sure it does not have any holes in it.

How would someone get started doing this.  Some of you may recogonize I am looking at creating some trade areas.  What geoprocessing tools might be helpful in accomplishing this?