The Story of Cloud and Seph...SPOILERS

[Masamune·1600]

A few corrections and clarifications.

The Beginning - The Centra traveled the world looking for "the promise land" which was a place that had a great deal of lifestream energy.

This is slightly inaccurate. For the Cetra, the Lifestream itself was the Promised Land, as opposed to merely an upwelling of Spirit Energy. This is due to the nature of the Lifestream; it embodies the afterlife, and, perhaps more importantly, the end to and fulfillment of their journey. The words of Elder Hargo in Cosmo Canyon clarify this.

Elder Hargo: There is no one place called the Promised Land. That is what I believe. No
no, it does exist. Hmmm... You can say that too. In other words, it doesn't
exist for us, but it did for the Ancients. The Promised Land is the resting
place of the Ancients. The life of the Ancients is one continuous journey. A
journey to grow trees and plants, produce animals, and raise mako energy.
Their harsh journeys continued throughout their lives... The place they return
to after their long journey... Their burial land is the Promised Land. Huh?
Supreme happiness? I believe that, for the Ancients, it was the moment that
they were able to return to their planet. At that moment they were released
from their fate, and gained their supreme happiness...

The Lifestream as a physical location of energy would have embodied the Promised Land from the perspective of the Shinra, as they were interested solely in the material benefits associated with a Mako-rich, materia-laden region.

Scarlet: Wow!! That's amazing! It's all Materia!!

Rufus: The outside is rich with Mako energy. The inside is a treasure grove of
Materia. This truly is the Promised Land.

It is a place o Eventually Jenova (an alien) falls from the sky and creates a large crater (the Northern Crater).

Again, the Promised Land of the Cetra is not the north of the world. It is the embodiment of the abstract notion of what is, to them, "supreme happiness," and is in a sense all the world at once.

JENOVA did fall to the location known in the game as the Northern Crater.

Jenova starts killing off the Centra with a virus until the Centra fight back and seal her away.

While "killing off" would have the same effect as what actually happened in terms of lowering the Cetra population, JENOVA did not actually bring about the death of the Ancients. Rather, those who encountered "the virus" were transformed into monsters.

From the Icicle Inn tapes...

Ifalna: I'm all right... When the Cetra... were preparing to part with the
land they loved... That's when it appeared! It looked like... our... our dead
mothers... and our dead brothers. Showing us spectres of their past.

Gast: Who is the person that appeared at the North Cave? I haven't any idea.

Ifalna: That's when the one who injured the Planet... or the 'crisis from the
sky', as we call him, came. He first approached as a friend, deceived them,
and finally...... gave them the virus. The Cetra were attacked by the virus
and went mad... transforming into monsters. Then, just as he had at the
Knowlespole. He approached other Cetra clans...... infecting them with... the
virus...

After that the Centra, who are severly low in numbers at this point, focus on helping the planet recover from its wound.

As suggested in the Icicle Inn tapes, the Cera had determined to do what they could to aid the Planet in the brief interval between the scarring of Gaia and the appearance of JENOVA.

Ifalna: 2000 years ago, our ancestors, the Cetra, heard the cries of the
Planet. The first ones to discover the Planet's wound were the Cetra at
the Knowlespole.

Gast: Tell us Ifalna... Where is the land called 'Knowlespole'?

Ifalna: Knowlespole refers to this area. The Cetra
then began a Planet-reading.

Gast: Ifalna, what exactly does Planet-reading entail?

Ifalna: ...I can't explain it very well, but it's like having a conversation
with the Planet... It said something fell from the sky making a large wound.
Thousands of Cetra pulled together, trying to heal the Planet... But, due to
the severity of the wound, it was only able to heal itself, over many years.

Gast: Do the Ancients, rather, the Cetra, have special powers to heal the
Planet?

Ifalna: No, it's not that kind of power. The life force of all living things
on this Planet becomes the energy. The Cetra tried desperately to cultivate
the land so as not to diminish the needed energy...

Gast: Hmm, even here so close to the North Cave, the snow never melts. Is
that because the planet's energy is gathered here to heal its injury?"

Ifalna: "Yes, the energy that was needed to heal the Planet withered away the
land... then the Planet... The Planet tried to persuade the Cetra to leave the
Knowlespole, but...

Gast: Ifalna... Let's take a break.

Ifalna: I'm all right... When the Cetra... were preparing to part with the
land they loved... That's when it appeared!

Following the containment of JENOVA, there is no record of the actions of the Cetra. While they certainly would have done everything in their limited capacity to avoid weakening Gaia further, Ifalna acknowledges that even when they possessed greater numbers they had no real way to heal the Planet.

In short, it's difficult to truly appraise the actions of the Cetra between the sealing of JENOVA and the appearance of Ifalna.

Hojo and Lucrecia- Hojo was a scientist and so was Lucrecia, they were also lovers. Lucrecia got pregnant with Hojo's baby while Hojo was studing Jenova and so Hojo and Lucrecia agreed to inject the baby (Seph) with Jenova cells while it was still in the womb. The baby is born and Lucrecia dies and Seph is raised (unsure where or by whom it never states ingame) and grows up to be a soldier.

Lucrecia does not die; the suggestion is inherently contradictory, because it is her appearance which triggers the flashback where this information is revealed.

Cloud's beginnings - Cloud was born in Niblehiem and grew up there with Tifa and all that. He felt he was weak and that Tifa would not like him since he was weak so he desired to join Soldier and become strong like his idol Seph. So he leaves Nibleheim and goes to Midgar to join Soldier. Unfortunatly for him he is too weak physically and mentally to join soldier so has to join the regular army (the blue dudes with the funky helmets).

It doesn't make sense to assume that Cloud was unable to enter SOLDIER because of any sort of physical deficiency, given his almost otherworldly combat prowess. There are only two reasonable conclusions as to his failure to enter SOLDIER: that his self-doubt was determined to be to crippling for entry, or that extremely limited exposure to JENOVA cells showed that he would be unable to function properly when fully injected. The second scenario seems more likely to me, given that such injection is an unavoidable element of becoming a member of SOLDIER.

Cloud: I'm physically built like someone in SOLDIER. Hojo's plan to clone
Sephiroth wasn't that difficult. It was just the same procedure they use when
creating members of SOLDIER. You see, someone in SOLDIER isn't simply exposed
to Mako energy. Their bodies are actually injected with Jenova cells...... For
better or worse, only the strong can enter SOLDIER. It has nothing to do with
Jenova Reunion. But weak people...... like me, get lost in the whole thing. The
combination of Jenova cells, Sephiroth's strong will and my own weakness are
what created me. Everyone knew that. I'm...... Cloud. ......the master of my
own illusionary world. But I can't remain trapped in an illusion any more......
I'm going to live my life without pretending.

It's worth noting that Cloud himself acknowledges that he is physically built like a member of SOLDIER.

Cloud Nibleheim Mission - Cloud befriends a young Soldier 1st class named Zack while in the military and 5 years after leaving Nibleheim he goes back on a mission with Zack and Seph.

Actually, Cloud leaves Nibelheim seven years before the events of the game, and returns to his hometown on that fateful mission five years before the events of the game. In short, he had only been absent from Nibelheim for two years at that point.

They are to inspect the reactor on Mount Nible. When Cloud gets to Nible he is so ashamed that he wasnt strong enough to join Soldier that he hides behind his helmet so that Tifa wont recognize him. When they get to the reactor Seph and Zack discover a bunch of pods with people in them. The pods are filled with mako energy and each person in the tank has had jenova cells injected into them.

They may have had JENOVA cell injections in addition to massive Mako exposure, but it is never explicitly stated.

Cloud: Wh…what is this!?

Sephiroth: Normal members of SOLDIER are humans that have been showered with
Mako. You're different from the others, but still human. But, what are they?
They've been exposed to a high degree of Mako, far more than you.

Cloud: …is this some kind of monster?

Sephiroth: Exactly. And it's Hojo of Shinra that produced these monsters.
Mutated living organisms produced by Mako energy. That's what these monster's
really are.

It's entirely possible that they had received JENOVA cells, given Hojo's penchant for shooting everything up with them, but there is no indisputable evidence of such.

Zhang (the martial arts dude)

Zangan.

As Seph is walking across a bridge over open lifestream Cloud comes up behind him. Seph stabs him, Cloud overpowers Seph and throws Seph off the bridge and into the mako.

There's nothing actually inaccurate here, although Sephiroth actually jumps into the Lifestream in Last Order (I myself have some issues with that retelling). It's worth noting, though, that Sephiroth has the head of JENOVA with him when he plunges into the depths of the reactor.