If you wanna do it right, buy a sub and then build a box according to the ts parameters of the sub. Buying a "good for all" box is just wasting your money on everything you bought because it isn't what you need. Truthfully, you are asking this question in the wrong forum. You are getting decent answers here but there are much better answers on a car audio forum. I just got done adding a sub to my regal and I spent over a month just designing and building the box for the sub. With something done right, you won't need a 15 or 2 subs. Like said above, too much bass without upgrading your main speakers will destroy your sound quality. And buying name brand amps will only get you an empty wallet. There are plenty of awesome non-mainstream amps that will put the big name brands to shame and cost less. Never pay for a name.
