That's a pretty cheap find on the subs and amp, but take a closer look at it. The amp says it's rated at 1700x1 @ 1 ohm, and 14.4V. First, your power is going to be around 12-13V unless you have a cap to add a little more power. Second, this is PEAK power. Those subs require 1500 watts RMS and 3000 watts peak. Will it still work, of course, but are you getting the most pound of the subs, not even close.
Also, look at the brand of amp. Why is it that a Hi-Fionics 1700 watt amp costs say $300 and a Kicker 1000 watt amp costs $500? It's because the Kicker is going to produce a true 1000 watts, where as the Hi-Fionics is not. I had a cheap amp in the past and when I hooked up a Rockford Fostgate amp with a little less power, I got 10x more bass out of it. So I would try and stick with a Kicker, RF, JL Audio, something along those lines. To get that spin busting bass your going to need some serious power going to the subs, so I would not skimp on the amp, JMO.
I agree with draft6969 that you won't need a new battery. I have two amps running off of my stock battery. If you notice your headlights dimming you can pick up a 1 farad cap for $75-100, or get one used on ebay which will eliminate the problem. But you should be okay without one.
Regarding the box, if you can make one your self, go for it. It will be better tuned to your specific subs, and you can make it so it fits how you want in the back of your jeep, etc. Plus you can get some color matching carpet from one the online stereo sites so it will look a lot nicer. I picked up gray carpet for like $10 and when people look in the back of my Jeep they can't even tell I have a false floor, they think it's stock.