So far in my car, I have :
Front Doors: MBQ components(DSD213 box says it can handle 90watts RMS) (5.25")
Back Doors: Nothing
Trunk: A pair of 12 inch w0s with 500 watts (500/1)
Head Unit: Alpine 9830 (50x4)

1)I'm gonig to get an amp for the front door speakers, just haven't came around to do so yet. What amp should I get for maximum performance out of my MBQ's?

2)I'm lost on what to do with my back doors, whether I should get a pair of woofers or maybe even a pair of 8 inch subwoofers to supplement the 12w0s.

PS - im looking for a balance of SQ and SPL with a slight favor towards the SPL.