Crisis and the events that spun off from it (including John
Byrne's
revamp, Lois and
Clark, Superman Adventures and especially Dan Jurgens'
"Death of Superman") do not exist. If you
want Superman to have died in your story, see
Last Son of
Krypton, chapter 25, or Jerry Siegel's
"Death of Superman" story
for indications as to how such an event would more likely have occurred.
Superman has an IQ of at least 3 digits, possibly more.
He is optimistic and self-confident. He does not need to breathe
in space and does not need a space-suit or space-ship for interstellar
travel.
Superman is Superman and Clark Kent is an assumed identity - his
facade.  The disguise of Clark may be vivid, important, and beloved
to Superman - but Kal-El's true nature is that of the Hero.
Clark has depth and preferences and structures of belief that grow as
he grows older but they are all constructs of Superman's obsession
with him. Clark is Superman's hobby and his template for humanity.
Superman was at some point Superboy. The child is father to the
man so for Superman to be the great man beneath the glasses and the timid
facade, then he has to have been such a person in his most formative years.
Jonathan and Martha Kent are dead. Their death marked the
turning point at
which Superboy became Superman. Like every
true hero of classic mythology, Superman has no parents to run to
seeking advice that he shouldn't even need. If you really want to write
a story in which Kal-El or Clark needs
guidance from Jon and/or Martha, you may want to consider making it a Superboy story.
As Superman grows older, his powers, capabilities, and wisdom grow as
well.
Whatever his age, he is moral righteousness - he knows what is right and
he does it.
Kal-El was born on Krypton, not on Earth. Further, Krypton was
an ideal, wonderful and advanced (in countless ways) society.
Superman honors and cherishes the memory of Krypton, not just because
all things of beauty should be treasured, but because the values and
strengths of Krypton's society are the foundation of Superman's
character.
Superman is not just some big guy
with a lot of powers. He is a shining example of all
that is worthwhile in humanity. His morals are also Super.
He is an inspriational and aspirational role model -
every true Superman story uplifts both the
character and the reader.