Brackets are required for the front, and you should go with the biggest speaker you can get in there. 6.5 vs 5.25 is a huge difference (50% more surface area) in the low end frequency you can achieve. It will NOT be louder - it will simply give you better sound. So if you can put a 6.5 in the rear, do so. If you can figure out how to put 6.5 in the front, do it there to, but expect it to be a PITA.
Easiest option is 5.25 all around - adapters are available and no modifying. 6.5 in the back is an easy mod, and well worth the upgrade - nothing to do with distance to your ear, all about frequency response - 5.25 simply don't play very low (6.5 don't either, but substantially lower than 5.25). Add a 10" powered sub in your console to fill out the music.
Pods are interesting, but not required. A pod will certainly improve the sound of the 5.25 as it will turn the speaker from a free air to a sealed box, which will make the speaker more accurate and less muddy. Foam pods will have some of the same effect, but not all as the "sealed box" is now flexible.
I like the Polks myself, but that is a matter of personal preference - go to a store and listen to different brands. They won't sound like that in your car, but the bright ones will still be brighter than the others, etc.
Lastly, get an amplifier. The factory head unit is grossly underpowered. Most amplifiers these days have high level inputs but check anyway to be sure. 4x50 is more than sufficient for most people, but if you can find the space, 4x100 or even 4x150 is better if you run with the roof off. Do NOT worry about matching the speaker rating to the amplifier - just make sure the amplifier is higher than the speaker. I know, that sounds counterintuitive, but it is all a matter of providing clean (unclipped) power to the speakers. It is highly unusual to blow a speaker by over-powering it.
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