Amp x can always work with sub b, it just depends on what you are looking for.

The subs you have can handle more wattage, if you want to up the wattage on the amp. Or, if you want to keep it the way it is, you can do that too. You've got 600 watts (I'm guessing RMS, since you have max RMS) to feed the subs, and that is fine. You can give them more if you want them to be louder but it is not necessary.

You shouldn't need a new battery, it wouldn't help anyways. If you are having problems with your lights dimming, the you need a higher output alternator, but I doubt you have to upgrade your electrical system for this.

As for the enclosure, can't help you out there, I usually build my own. Costs about 30 bucks

Edit: just saw the previous posts, and unless those subs come in a different resistance, you are only going to be able to get about 300 watts out of that amp. Still will work, but only half the watts.