When updating an app iOS prompts for password to a completely different, not yours AppStore account.
If your iPad or iPhone does not detect headphones and output sound to the speakers even though the headphones are plugged in, or vice versa, just shutdown the device and then power on it again with the headphones still attached.
All iPads within the same product line share the same platform. That means, that means you get the same performance regardless of the built-in storage flash memory capacity and the 3G/4G modem. But what exactly are you missing by investing in the cheapest iPad 3 16Gb without 3G/LTE modem?