1. I believe the subs are only 150 watts rms each, so technically he is correct. I would buy a larger amp though so you'll have room to upgrade when you decide to. If the subs are in fact single 4 ohm you need an amp that does it's power at 2ohms. I would do as someone else suggested and find a Kicker 750.1. You could also get a brand new Eclipse XA1000 on
ebay which is rated at 480 watts for ~$80 shipped.
2. I would just borrow a circular saw, jig saw and a drill and build my own box if i were you. Prefabs like the one you linked are usually tuned way too high and poorly built but for $60 you could give it a try.