RE: how the electric system works?
Ummmm, kinda yes and no. Yes you need an esc to handle at least what the motor draws.
BUT and it's a big one. Depending on where your esc is located sometimes you are better off going with a higher capacity esc then your system demands. Remember how I said it's an on/ off switch? Well in the off position the esc has to get rid of the voltage it's holding on to rather then releasing it to the motor. This causes heat, and heat has to be dissapated or the esc will over heat and shut down or fail. A bigger capacity esc can handle more heat then a smaller one. But a smaller one will work if there is enough airflow over it to keep it cool, like on the SS. It's out in the air so you should be fine. But the same set up in say something like a Cub, where the esc and motor and even the pack aren't cooled as well could cause you a problem.
Now then 2 other things on an esc. One they are rated for the max amount of voltage they can handle, exceed this and all the magic smoke leaks out of them. 2 ratings on an esc one with the bec hooked up, one with it not. Incase you don't know the bec is a built in Battery Eliminator Circuit. It steps down the voltage to the 4.8 or 6 volts your receiver and servos have to operate on. And guess what it gets hot too, as it's bleeding off voltage to drop it down to run your system. Just another item you need to consider in an electric. Also the bec is limited to how much of a load it can handle, such as how many servos it can operate, again over load it and the smoke comes out.
Isn't this fun?
Another curve ball for ya, if your set up's bec can't handle the load, you can disconnect it. And install a UBEC, all it is, is a stand alone bec, just like the one in your esc, but it's a much heavier duty version. It will handle more servos and run everything except the motor, your esc still runs it.
As for your question about not worrying about what the pack is, no you need to throw that into the mix also. If it's too high of a cell count like a 4S pack, and your esc is only rated to 3 more magic smoke will fly. You'll either have to add a ubec, if your esc will handle the voltage with it's bec disconnected, or switch to a higher voltage rated esc.
Also just cause the voltage is correct, like your 3S, you also need to consider the other part of the battery ID, like I said about before, it has to be able to handle the amp draw from the motor, and provide it for the length of time you wish to fly before it hits it's cut off point.
Lastly, just because your motor has a max amp draw listed, doesn't mean that's where it stops at. Your prop size will affect it. So will the amount of cells you power it with.
Too big of a prop and motor will pull more then the max rating and the smoke will leak out of it.
You need a meter, it's the most important piece of equipment you can own. Like an Astro, or Watt meter. It's plugged between your pack and airplane, when you run up your motor it's going to give you all you need to know about your system. How many amps it's pulling at WOT, how much the packs voltage is dropping, how many watts it producing, and so on.
With out these figures your are flying blind and something bad is going to happen.
And after all that you'll find out specs are sometimes way off the mark. Mfgs built in a safety factor sometimes. And sometimes you can exceed them and get away with it, sometimes not.
Heat is the enemy to electronics, eliminate heat and you'll be surprised at how far you can go above what the specs say you can.