I have 6 1/2 focal separates, Kenwood 4x6 plates in the rear pillar and 2 10" punch, alpine amp for the front and back and punch amp for the subs.
I had gone the route of not using amps or subs, i would definitely bought different speakers and not gone high end. Focal cost me almost 200 and the 4x6 cost me about 80.
I would set my budget of 150 dollars for all the speakers give and take a few bucks. Reason why is your stock unit is the limiting factor. Try to keep the front at 80 and maybe the 4x6 at 50 dollars. Get with Crutchfield to get an idea on quality and price to what works for your budget. At least you can compare them side by side in performance and price. There is an aftermarket stock radio thats new that incorporates a usb port and Bluetooth connection. Looks like our stock radio but inside are all modern, not sure the price but check LMC or one of them restoration site.