Never heard of a 10 inch sub sounding better than a 12 inch but i guess it all depends on what "better" sounds like to every person. i def would not put 10's in the bed at LEAST 12". I took a look at your deck and everything looks good about it but if possible try to find a Head Unit that has 5v pre-amp voltage. if your going for absolute awesome sound then 2.5v will hinder the capability of the system. Switching the speakers and subs off and on is actually pretty simple you just run the blue wire coming from the Head Unit to a switch and THEN to your amps that you want to be able to switch on and off. Sound Processors arent really needed it cleans the signal up that goes to your amps and speakers but since you are using an after market head unit, they are pretty much like crossovers, also if you want the best sound from your speakers look into Component speakers since they come with crossovers already( a crossover will split the frequency's of the signal so the bass driver gets the lows and mids while the tweeter will get the high frequency's). The Next big part and the most important is your amps you need to spend alot of time researching every amp you look at please do not get the knock off amps you find on ebay or other sites that say they can put out 1,000,000 watts for only 200 dollars lol, stick to name brand amps (MTX,Audiobahn,Rockford Fosgate,Kicker,etc.) You also might find that you need to run one amp per sub since there are not a lot out there that put out high wattage to Dual subs on a average impedance (2,4), also check to make sure your amp and subs have the same impedance, when you start to purchase and wire the subs and amps then it gets a little confusing with how you need to wire them ( parallel, series, a little of both maybe?) i would buy the best amps you can find, and THEN buy the subs. With subs, Impedance is a very important thing it will either make or break your system. Doing subs is a whole other chapter of audio systems and would probably too much to handle at this time haha. So start getting a list of the speakers you are thinking of getting and stuff like that and then well all go from there