as for the speaker size question...if you are fiberglassing and customizing the mounts, it doesnt really matter. theres quite a bit of room behind the stock speakers. i am going to caution you though: it seems like you have a massive install planned but dont know much about what the hell you're doing. please, please, please start off small and work your way up...otherwise you might end up with something that looks and sounds like shit (assuming this is your first big install).
another hint on staying rattle free: wrap and secure a thin strip of felt (or similar) around the "bar" that the latch secures to in the trunk. this will hold the trunk lid down tighter. in my old car, i also adhered a thin layer of matching carpet inbetween the edge of the plastic interior pieces and the metal they touched. this eliminated every rattle i had, especially the ones from the plastic trim in the hatch. if you make really clean cuts and color match the felt/carpet/whatever, its unnoticable.
