2. This is a joke. "Intel inside" is a famous slogan for Intel microprocessors: you may have a sticker on your own computer proclaiming "Intel inside", meaning that your computer has an Intel processor. The "idiot outside" is the joke, and refers to the person operating the computer. For example, somebody might complain that their computer does strange things, and you might discover that the fault is not the computer, but something the user did to the computer. Later you might tell me, "The problem was: Intel inside, idiot outside."
3. Take a good look at him/her.
5. The expression "He was head and shoulders above the rest" can be quite literal -- he was so tall that his head and his shoulders were above everyone else's heads -- or metaphorical -- he was far better than the others. Head and Shoulders is also the brand name of an anti-dandruff shampoo, so called because it stops dandruff from forming in your hair and falling down onto your shoulders.