What I was trying to say is when you create a definition query to extract those parcels that have an area of 1 acre, you should not use area = 1 (if he unit is acres) but something along the line like:
area >= 0.99 and area <= 1.01
This will use a tolerance of 1 percent. Change this according to what you consider right. You can use the "Select Layer By Attribute tool".
Next step would be to use the "Dissolve tool". Dissolve all polygons (don't select any "Dissolve_Field(s)" and uncheck the option "Create multipart features").
The resulting featureclass can be used in the Select Layer by Attribute tool where you can select for areas larger than 5 acres. I assume you use featureclasses in a geodatabase (and not shapefiles). If you do use shapefile, you will have to add the area field yourself. See ArcGIS Help (10.2, 10.2.1, and 10.2.2) for help on that.
Once you have the remaining contiguous polygons (dissolved ones) you can start you development analysis for these locations.