The closest you can get to is the New Age faith, note that every single God that was believed to exist may actually in fact exist or may not exist along with everyother mythological figure.
The truest faith is to be open to new ideas and concepts in the idea that they could be the truth with so many evidence with many supporters/believers in them.
One religion will never happen until the real proof is finally confirmed worldwide instead of personal revelations from pyschic mediums, ghostly encounters, past life rememberers, modern day "prophets" (or at least kinda close to), Marian apparitions, and other Sainty or Godly appearances/miracles that have their own believers and backlashers.
The world is awaiting this confirmation by the obvious idea of a Jesus/Messiah person clearly gaining people's attention by flying in the air with hoards of angelic or godly forces behind him as every person can now bow down to him even if they never walked.
The world must be warned of the prophecy of evil that could be an Anti-Christ claiming to be Jesus or better than Jesus who will try to create his "One World Religion" however he cannot summon angelic forces as I would think Jesus would be able to do as with my denial to all
Jesus Claimants, who in prophecy were told to "decieve many".
It is the idea of being decieved that people might not want to latch on to a faith in the idea of fear that it will prove to be false.
Now let me actualy answer your questions directly:
What would this religion need?
*This religion would need mass miracles to make it hard not to accept as fact.
What sort of symbology should be used for mythologies or stories of the religion if there are any?
*Many symbols would have to used like any statue or painting to symbolize the religious figure or event.
Should we take true examples from the past or make up ideal examples?
*That matters on the doctrine of faith, sometimes old stuff mostly connects with modern day but things get changed like we don't stone people for adultry.
Will we wait for stories to unfold after the religion is open rather?
*Oh yes we should wait for the stories to unfold with some angelic or Messiah figure clearly stating what is true, what isn't, and what can be added or subtracted from doctrine.
What do all religions have in common?
*The idea of faith and hope for their ideals to overcome everything that goes against them.
What should their book be called?
*Matters how long their books are, suppose Jesus or an Angelic figure writes a new Gospel, and then more Holy figures are up to it and perhaps 20 new books for an official 3rd Testament are written. A "3rd Testament" is ideal for major works of Holy people near our time after the 2nd "New Testament", but they could call these New Gospels anything, perhaps even "The Bible 2" if new material is long enough.
So what would people enter this religion for? Why do people enter religions or turn to religions?
*Well if it is the exact truth, they all wouldn't want to deny what is strictly obvious as seeing all these Holy people in the public eye. In today's mortal senses, people enter or turn to religion in seeking hope or feel a pressure to enter. Atheists must note an idea of "What if there is a Hell, and I need to be saved?". There is hope in Heaven, a victory over all evil, and pure universal love.
What uses do religions have besides moral values and answers? Why do people need answers?
*People need answers because they question everything that can't understand, like most Holy stuff isn't exactly a day-to-day basis to where it is universally accepted that faith is real. People do not understand unless something happens to them that makes them believe (
like the once Atheist doctor who claims he died and went to Heaven only to be brought back).
I am basically wondering what is the ideal most accurate and acceptable least restrictive religion possible? What would it be like? Don't say your religion, thats not the purpose of this discussion, or if you do at least provide reasons why they are ideal in certain circumstances.
*Well I am sorry to say it, but it is my New Age faith that is the least restrictive religion in the world. You don't have to believe in a "female goddess", you don't have to believe in the Theosophical "ascended masters", and you don't have to believe all the other different aspects that the New Age faiths hold as doctrine. It is the most accurate with having the most topics of discussion spanning multiple faiths interwoven into one with most aspects being accepted.
Do you think this is a waste of time?
*No I think you raise a interesting question of what if a "One-World religion" were to actually arise, either my idea that Super-Supernatural events must occur or someone else may say much different than I would and claim all it would take is someone like a new Mother Teresa or a possible Buddha or a new "world teacher" which can prove something divine enough to get all of mankind's attention. I would think more topics like this being discussed would be interesting.