Do yourself a favor and do some research on power requirements for whatever you plan on doing. Unfortunately I didn't do my power research and I'm now shelling out an extra $400 for new wiring, Big 3 upgrade, new battery, possibly new alternator, etc. Don't run into the same problems I did....
Keep in mind if you add a lot of amps (wattage, amperage, voltage, whatever), you're going to have electrical problems. You will most likely need to double-ground your battery and your alternator depending on what you're getting. Also, alternator positive to battery positive via a fuse. From what I've gathered through my research, your car's stock electrical system was designed to handle ONLY what the car and its electronics pull, and not for any aftermarket audio equipment. I've run up to 600rms without grounding my battery or alternator, but anything over that you should consider it. You may not neccesarily hear a differnence once you do your big 3, but it should help your alternator last longer if you're pulling more power than necessary. Also make sure you buy a Digital Multimeter to set your gains properly because it will assure correct power draw and you won't blow your expensive equipment.
I learned my lesson: post threads before buying equipment....
Also: if you're going sealed, you can build/box a pre-fab box. If you're going ported, BUILD YOUR OWN BOX, or pay someone over $150 to build one for you properly, there is no easy way around this. How good your ported sub sounds depends almost 100% on the quality, size, weight, thickness, and porting of the enclosure. Good luck!