some great advice I am able to give is to goto sites like the following,sign on for a free account,and spend a month reading topic after topic......
Get a good understanding of how to build a system,learn how an amp works,how to tune an amp,how to match the amp to the subs and their output,find out what ohms and watts are and you will be on the way to buying the right materials.
For instance if you buy subs that take 1000w and you have 3 of them,how many watts amp are you gonna need to properly power them,what ohms do they need to be,how do they need to be wired.
there is a lot to learn,but it is kinda easy,but first you need to read and read and read.
The site I supplied is the one my friend directed me to about a year ago......I spent a month reading and still go there weekly to read and honestly can install with good understanding any amp and sub and comp setup with no distortion or risk of blowing any equipment.
3 12s is gonna be way too much to fit in a tC,gonna take a lot of power and a lot of box,3 10s is pushing it in a tC.
A direction to get you started is figure out the number of subs,figure out the total wattage they can handle,figure out what ohms they will run at if you wire them parrelle or in series,figure out the ohms they can do if you use a D2 or4 sub......once youhave those numbers match an amp to the setup.This is the first step.
Then you have to figure out sealed or vented box and will the subs I have picked sound best in one or the other.
then you can move forrward form there.
It is easy but when I see people say they do not know what is better 2 or 4 ohm subs it says they will bloy up their system ina matter of a couple of months and have spent hundreds of dollars on door stops.
To answer that question though neither is better than the other,speaker ohms are just the operating resistance fo the speaker........nothing more,there are no differant performance gains from one or the other.
A D2 500w speaker sounds the same as a D4 500w speaker form same manufacturer,jsut made to work in differant power application.