6) As a general rule of preference, I dislike dice and victory points
The game will be card-driven.
2) The game cannot be very restricting and linear. Part of the fun in the idea of time travel games is that you can have unforeseen consequences in your actions.
The simplest way to make sure that the events of the timeline are not too linear is to change how they are related. The hypothetical world this board game will take place in can have levels of W(ar), C(ulture), and T(echnology) for every Era. Every event card will have two sides, with one representing that the event happened, and it's flip side representing that it did not happen. There would be requirement stats that would determine which side would be in play. For example, you might have a 1936 Olympics card, with a requirement of 5W and 4C resulting in the Olympics taking place in Berlin. This in turn might generate certain levels of W for the next Era. But if the W levels were less than 5, or the C levels were less than 4, the 1936 Olympics card would be flipped over, and would take place in Spain instead.
Overall, no events are directly linked with any other events.
Thematically, this actually works out pretty well. WWI is widely agreed upon to have been sparked by the assassination of Archduke Frans Ferdinand. But would WWI have occurred if the assassination didn't happen?
Probably! All the pieces were in place, and stopping the assassination might delay it, but not stop it altogether. All this would thematically reflect time travel in a universe with Rubber band history. Changes to the past get smoothed over as time passes, and big events are hard to prevent unless lots of changes are made.
*All examples used are arbitrary, and I don't intend on using real events like the 1936 Olympics. War, culture, and technology aren't set in stone either.