I'll help you out here as much as I can since I'm very bored =P
Ohms-Basically the resistance power faces when it's trying to get from one place to another. More ohms=more resistance. So say you've got an amp rated at 100 rms at 4 ohms and 200 rms at 2 ohms. You get more power because you have less resistance. Not totally sure what RMS stands for but it's the actual constant rate at which your amp puts out power. This number should be the power number you look at when considering an amp to buy.
Now I'm not totally sure on the reason behind the next part, you'd have to ask a physics major, but the way you send current can either increase or decrease the ohm load. If you have a sub with a 4 ohm dual voice coil (dvc) that means you can run that sub at either 2 ohms or 8 ohms resistance to the amp. This all depends on how you run the wire to the voice coils. You can see diagrams for all the different wiring options
here.
Channels on the amp are just for the left or right speaker/sub outputs. If you want to be able to control balance to the left or right of your car you would have to set this part up correctly on the amp (right speaker to right speaker channel, left speaker to left speaker channel).
SQ=Sound quality
SPL=Sound Pressure Level (loudness)
Some helpful links to products you will probably be suggested:
Focal
Magnum d2 website
Avionixx amps
Elemental Design (eD)
Resonant Engineering (RE)
On-line stores are usually very cheap to shop at but often are not authorized by the company and therefor do not come with the company warranty. Some good on-line stores:
The Zeb
Sound Domain
I've heard a lot of complaints about these guys but they have a really wide selection of products.
On-line Car Stereo
A full list of online stores can be found
here.
Big box stores such as Circuit City and Best Buy can sometimes have good deals but their sales staff *NORMALLY* isn't as knowledgeable as you would find at a more specialized dealer.
When looking to purchase new equipment check out all the local car audio shops and listen to things, often times what sounds good to me doesn't sound so good to you.
People on this board are very willing to help, but before you post a new thread do these things first:
-Use the search function, a lot of the time your question will have been answered before.
If the search function doesn't turn up anything:
-Ask yourself how much are you willing to spend?
-Do you want SPL or SQ or both?
-What kind of music do you listen to?
-What other information do you think may be relevant?
Once you've got that all figured out post all that information plus your question and people will be very willing to help you out.
While still under heated debate, it is generally accepted that wire is wire and amps are amps. No reason to buy the fancy wire and as long as your amp is putting out a good rms and you don't need the extra features you don't need to spend the extra money.
Lanzar, Sony, Pyle and Audiobahn are not generally considered good brands. They CAN produce good products but all in all people aren't very happy with them.
There is no real way to tell how loud your system will get without measuring it.
Ported boxes are normally louder but with less sound quality.
Sealed boxes are normally a little less SPL a little more SQ.
Bandpass boxes can be good but they must be made very specifically to the sub you put in them.
Rear fill (speakers in the back of your car to fill the air) are generally accepted as a bad idea, your money is better spent on a good set of components for the front.
Kick panels are great for providing a little extra sound quality. Details on constructing your own kick panels can be found
here.
That's about all I can think of right now. I hope this helps a little bit.