@TXAG I forgot to address this. Speaker size preference is a sound preference; I have used both sizes in different Ford trucks. The rear speakers in my opinion aren't necessary unless you are going to do a complete audio overhaul. If you are going to go with the hideaway and not amplify anything else I would go with 6x9's, consider adding sound deadening material.
I would go with the infinity ref 9632ix or 9633ix 6x9's. They are 3ohm (I've measured 3.2ish give or take) the factory are 4ohm, this will give you a tad bit more volume but they also can be a bit bright. I would go with the Dayton DSP408 and the Kicker Hideaway 10. 8 gauge OFC install kit should be fine and like I mentioned earlier many companies or individuals offer a plug and play harness to add a sub/amp(s) without splicing or cutting. With the items listed above you should be under $800 total if you plan to install yourself.
My mid-tier system I plan to install on my 800a will be between $5,000-$6,000, doing the install myself and getting the system components at dealer cost. I like to stick with one brand of speakers/sub for a complete install if possible. I will attempt a single shallow mount behind my rear seat but it will be turned down unless the seat is folded down because I absolutely need the space. I will not move my seat or add any type of brackets. If I can't get the behind the seat sub to sound like I want then I will have to change it up. I haven't compiled a list of what I want but I will probably go with Focal, Audiofrog or JL audio in that order, use a high end DSP and an amp combo.
