We know the 5 travelled back to the 12 Colonies at "relatavistic speeds", with no FTL, to warn the humans not to build a nw race of Cylons, having themselves come to a sticky end and escaped just in time by using newly re-discovered resurrection, but were too late.
So, the Humans once created the Cylons on Kobol, it lead to war and a split. This was then repeated both on the 12 Colonies and the old Cylons' Earth. That makes the current Human/Cylon war the fourth.
We know that the 5 original Earth Cylons managed to bring about the 12 Colonies' armistice by giving the 12Col Centurions resurrection and the humanoid boidies they were already working towards themselves. The first of these new breeds was John (Cavil), who has deep seated instability and hates the limitations of an organic body. He turned on his creators, the Earth 5, and killed them, putting their resurrected bodies amongst the humans as a punishment and revenge. John also killed the Number 7, Daniel, though the explaination of why is not yet clear.
Having just watched the Caprica pilot trailer, I find it interesting that one of the main characters is called Daniel. I think it's Graystone, the creator of the robot copy of Joe Adama's daughter and Bill Adama's sister. My guess is that one or more of the Daniels survived. How this will fit though, seems difficult, as that Caprica Daniel was set prior to the war, and the information from Ellen suggests they arrived after the start of the war. If Tigh's memories of the Cylon War, including the Brinnock, are real, then maybe the Earth 5 arrived before the war with their 8 new models, and gave these models to the 12Col centurions as a peace offering? An what seems like Lucy Lawless in the last voice-over in the trailer... could this robot sister of Bill's become Number 3?
As for the Galactica itself, it seems odd that the structural damage is a surprise to the crew - surely the engineering teams would have been conducting regular inspections, given her age, her participation in two wars, four years on the run, some massive nuclear poundings and a freefall through atmosphere? I can't see any reason she should change in appearance at all for structural repairs - they'd just cut away and replace the bad steel pillars and plate the bulkheads. The only thing likley to chage her lines at all is the Cylon FTL system, but that might just consist of tweaks and modifications to the existing set, ather than and engine compartment rebuild. The organic compund to repair the steel microfractures could change the looks a little, I suppose - it could "eat" the paint and scorch marks' soot, cleaning the ship to an etched metal finish similar to the Raiders, Basestars and season 1 Centurions. If it's meant to be a sentient compound (hive mind, nanobots or whatever other analogy you like), perhaps it'll be a Trek-like end-of-episode reset with an as-new ship at the end of it. I think they'll resist that option, though, and just have it repair the microfactures only - if you have it sealing all the big cracks, it'll get silly; how would id differentiate between a crack in a beam and the joint between a door and its frame, or other moving parts?
