your best bet is to get a 4 channel amp for both front & rear speakers. This will give you better sound all around. As for the kick panel, it all depends on who builds them. I will be starting a set for my car soon. It takes a lot of time to build these (18 hours for my last car). there are videos out there.
www.metro-auto.com has vids from basic to extreme. same with
www.selectproducts.com. I have ordered one of there videos & it is very good. If you feel confident enough to build them yourself, this would be the cheaper way to go. They can run upwards of $500 a set without speakers. Good luck.