please help with an amp install

Ok. Due to the nature of my shop, I have done very few amps and could use a bit of guidance. A customer rolled in today with a 91 300zx(like new) with a bose system. We are going to eliminate the old bose system and replace the speakers, and I need to know what size amp to use. We are putting 2 10" subs in the rear and replacing the rear mids with Fosgates. The Fronts are Polks, his Kenwood head-unit has only one set of pre-amps. The rear mids ar rated at 50 Watts per speaker RMS. I'm also not totaly sure what kind of crossovers to use. Thanks.

i would highly recommend running 2 seperate amps, one for the speakers and one for the subs, get a high level input 4 channel amp with 400 watts max, 200 rms, 50x4. then get another amp to just power the subs, u wouldn't really need to buy aditional crossovers since most amps have crossovers built in, doing it with one amp would be expensive, u need a ton of power and alot of bass blockers, put inline, and that type of amp would probably be more money then the 2 seperate amps