u intend to run 4 speakers correct. 4" in the front and 6x9's in the back.
get the Pioneer D1002R 4" speakers for the front.
u will need a 4-channel amp if u plan on running 2 pairs of speakers. u can also buy a 2 channel but ul have to wire the speakers at 2ohm load. the only issue with that is, u will either loose the fader or balance adjustment from the pre depending on how you wire the speakers. so the 4 channel is the better option.
keep the rear speakers for now. once uv done the install, see how they respond with the current setup. normally the sound is staged at the front. the rear stage is used for a surround sound but requires additional equipment (and that isnt cheap) and cannot be achieved normally. however the best option is to run the fader 70/30 for the front/rears (how alot of people do it on normal setups). However thats entirely upto you.
for the amp, the best option is the pioneer 6500f. u can also get kenwood 4 channel amps in that range but u will havto do some market survey. or if u want a more sq oriented amp, try the addzest amplifiers that are up for sale here on pw.