Sounds as though your front stage is gonna be quite impressive with the amp/speaker setup you have chosen.
The rear fill is not as important as your front stage. Almost any mid-priced coax or even a low end seperate will be sufficient for rear fill duties. I have heard cars that have had no rear fill whatsoever and they sounded fine. I believe it is all a matter of taste regarding rear fill in smaller cars.
Tom Kenyon
Custom Sounds
San Antonio, Texas