Most apps aren't running in the background. They are suspended so they will resume quicker when you open them again. By killing processes you are using more battery when you open the again because the must be read from disk and then initialized.
You should only kill misbehaving apps. An app suspended in ram cost you nothing as it has to be powered no matter what. When you start running low on memory, which happens less on phones with this much ram, the is will free up memory by killing suspended apps.
This isn't windows mobile so don't sweat the apps. You will do more harm then good. Whether swiping them away causes them to be killed I don't know. You could swipe one away then go to the applications tab in settings. Find the app and see if the "Force Close" button is enabled.