You hooked me with your concept of an alternate timeline. If I could make a suggestion, often these RPs veer away from using canon characters, but due to your plot, the use of canon characters would be fascinating for you could see an alternate development for the character. Like what if Alistair, after the tragedy of the loss, changed from his good humored self into a far dark and ruthless Warden? If I were doing this I would allow the PCs to play canon characters if they wanted, just to emphasize that 'alternate timeline' feel.