I have some suggestions/comments regarding your amp/subs/x-over situation.
First, if moneys tight look at this website.
This site in my opinion is one of the most affordable websites to get all car and home audio wire, cables, power distribution, fuses, raw drivers ( including subs ), and any instalation accessory you need to design and install a great system. Best yet everything has a 45 day return policy.
As for your amp, I think soundstream makes a pretty good and their reference series was pretty solid. If the amp can handle it, you can run 2 two ohm drivers in paralell and be fine. You should run 12 gauge wire to the subs and use it in the construction of the box as well. This should only cost $2-3 dollars more because you should not need more than 10 feet of wire to install subs.
As far as the x-over is concerned, yes you can use a passive crossover or a coil to complete the install. You can find these at parts express as well. If at all possible try to spend more money on your crossover and less on the drivers themselves. The reason is passive x-overs can effectively reduce the output to your subs by 15-20%. Applying an active crossover will give you more flexibility and allow you to use more of your amplifiers true potential.
If you haave any questions, you can write me an email.
That's just my 2 cents, feel free to give me change, and good luck.