Frankly, I would explain it, but that would require me to be able to keep Sonic in one place long enough to actually examine the inner workings of his head. This hasn't succeeded as of yet, so all I can provide you with are theories. And frankly, each is more unlikely than the last.
The only theory that holds some water at present is the fact that Sonic does have two eyes, but a unique ocular structure in that his pupils are independently mobile in a larger single eyeball. This enables the same necessary movements that other beings have. Just in one eyeball. Doesn't really serve to answer the question as to how that eyeball would fit in his head alongside his brain and other necessities, so the theory could be expanded into suggesting that the oculus in this matter is, in fact, a membrane filling his entire head, containing the pupils, but also the brain and other necessities.
But frankly, I can keep on theorising like this and learn little. Biologically, Sonic is an anomaly. That's the most factual answer I can give to this question.
That would explain it. I'm not quite sure why SEGA decided the handheld version of the game needed a different storyline, especially as the events chronicled in the console release are accurate. On the matter of Chaos, you make a fair point. I merely misinterpreted your point of view about Chaos because it's fairly obvious that its power is devastating. A couple dozen scuttled plans and fleets are a fair indicator of this. And in fairness, Metal Overlord didn't exactly go insane. The protocols were all designed by me, but Metal Sonic was designed a little too single-minded. He was focused on the objective of beating Sonic to the exclusion of all else. Technically, he didn't betray me at all, but carried out his programming. Of course, Sonic still beat him, but I've since gotten Metal back into the fold. I'm rather fond of him, really.
1 - These tablets were found in the ancient ruins of Knuckles' ancestors back on Angel Island. The tablets only spoke of Chaos' immense power - remember, they couldn't really warn about what happened, because the event of Chaos destroying everything was actually the destruction of that clan. They could hardly have then built a huge intricate mural inside their biggest temple after being decimated. Plus, I've dated that mural to a time earlier than that. That is why the clan wanted the emeralds. They knew they could gain some power from them, possibly the power of Chaos.
Of course, this too is all conjecture, but it makes more logical sense. It is, however, fact that the mural is older than the destructive events.
2 - I live on one of the most sophisticated technological constructs known to the world. Suffice it to say that I can regulate how warm or cold it is inside the Egg Carrier.
3 - Sonic can run faster than the speed of sound, and you worry about Tails using twin tails as a propeller? And it's certainly possible, just quite difficult. Tails managed to learn to fly with his namesakes, and well done him.
4 - I have no idea, and to be perfectly honest, I'm a little afraid to find out.