Dont ask us, just go to that local car audio shop and pay for a system and get something that pounds. Don't go into that long lame ass story either.
You should be able to get a cheap deck and cheap speakers with the $225 gift card, and the $400 should get you some entry level subs and amp combo they might have on sale. Let them install it and get a reciept with warrenty on the products and install. Then get a car alarm.