Optimization in blender side
(in the moment i can remember of these) :
1-Reduce faces using Decimate modifier in blender.
2- Remove Double Vertices. [go to edit mode → select whole mesh → hit W → select remove doubles]
1- Use LOD generator to reduce vertices when looking model from far distance
2-Use instancing. (only for non animated models, i think)
3-Batch Geometries (again for non animated models) .
well… the problem is more the “100 characters” than the number of polygons…
Are they all visible at once?
1000 polygon can be very ugly if you have some close ups, 4000… is okish. Also you may want to look into the lod generator and the LodControl, it can help you to display less polygons according to the distance to the camera, and keeping your 4k tris models.