40-70 is a big range i think......
since both the players take the damage
theres a high chance that it can be a tie
and do they both take the same damage?
I guess I would make it so the damage is dealt first to yourself, and then to your opponent. (So both die is a loss)
Yes, I would want the damage to be computed once, and applied to both players.
The big range is quite intentional. If the range is small, I think it synergizes too well with a fire (or cremation rainbow) rush deck. Done this way, you run a good risk of dying if you decide to nuke the world.