In most examples of Conways game of life, the grid wraps around meaning the leftmost cells are neighbours with the rightmost cells (since we don't have an infinite grid). 

Do we use this interpretation here? If so, it might be a good idea to clarify this in the rules, so we can directly compare solutions, since wrapping around adds additional complexity.

I'll leave that decision up to you! It might even be an interesting exercise to have a toggle to turn this on or off to see how much overhead this introduces for your implementation.

Not necessarily it will be more expensive. You do not have to test for the edge so no branches are necessary.