Just thought I might start a thread on this, because these are details that should in theory be hammered out before the onset of a full on franchise.
My Perspective on Superman's Powers:
there is no magical forcefield, or energy field that his body produces that give him his powers. His powers are a result of nothing more than his advanced physiology and his ability to absorb energy through sunlight, rather than ingesting food. So starting in order of appearance:
1) invulnerability: superman's first power. Superman is not literally invulnerable, but rather, his 'flesh' is made of some material that is far more impervious to damage than normal human skin. Looks and feels the same as human skin/flesh... but it is infinitely stronger, resistant to damage and resiliant. He is invulnerable because he is made of stronger stuff than us, not a force field. Inborn power
2) strength: superman's strength is a function of his ability to absorb sunlight. Simply put, the larger his store of energy, the greater the output of muscle strength: see invulnerability, he is made of better material than us humans. However, this is a power that requires larger amounts of solar charge... meaning it takes his young body a number of years before he can start displaying superstrength. He is super strong because his muscles are made of stronger stuff than us, coupled with growing solar energy stores. Inborn power, that requires energy, will develop over time
3) speed: pretty much the same as strength. His speed is a function of how charged with sunlight he has become. Over his childhood and youth, his speed would slowly grow until in adulthood he is superfast. He is superfast because his physiology, muscles, nerves etc. are made out of more advanced material than us, coupled with growing solar storage. Inborn power, that requires energy, will develop over time
4) Supersenses, Superbrain: He's born with these outright. They don't need to develop as his other powers, they are always on. Just like a dog's ear can hear more than a human's ear, Superman's ear can hear more than a dog's ear can. Just like humans can only see visible (to human) light(the rainbow), Superman's rods and cones are far more advanced, and therefore see a greater spectrum of radiation as 'visible' (obviously all the way up to X-rays, don't know about the other direction). Microscopic and macroscopic vision is a result of his cornea being made of the same advanced non human material that his body is made from... allowing for greater focus and zoom.
most importantly about these, which was touched upon in SR,,, Superman cannot turn off these senses. They are not magical on off powers. They are always operating, but superman's brain is able to deal with the greater amount of info that his senses are delivering him. Moreover, his brain is also 'superfast', otherwise when moving at high speeds, he would be bumping into everything, ie. he has to be able to think faster than he moves.
His sight was well explained in Superman: Birthright, and his hearing was well explained in SR.
These are all inborn powers, they do not develop over time, he always has them.
5)Flight: IMO, superman's ability to fly should not be a result of some magical energy field that makes him float. But rather a result of his superspeed. flight should actually be one of the first powers he begins to have, as this would offset his emmense weight (generally, materials that are stronger, are also more dense, and heavier). However, as his solar storage grows, and his superspeed grows, Superman should be able to vibrate his body in such a way that he can actually defy gravity, but this would all be happening so fast, that it would not be visible to the human eye. This would mean that Superman's flight is more like swimming in air, rather than actually defying gravity. A result of his inborn superspeed ability, requires energy, and will be available as actual flight, rather than offsetting weight or long jumps, when his energy stores have reached appropriate levels
6)heat vision: this is the only power that really lacks any explanation. He just has it. But it requires the highest level of charge from his solar battary, and is therefore one of the last powers he should develop.
That's my perspective. No magical energy fields and what not. Just that his body gives him these advantages. And that in order to power that body, he must absorb sunlight. He is stronger, faster, tougher, more sensitive than us because of his physiology and the material he is made up of.