Like all +1 weapons, the DM will add +1 to the AC hit when using this weapon but the damage bonus has already been factored into the damage wheel.
A heavy crossbow takes one combat round to load after being fired. Therefore, a player using any type of heavy crossbow (mundane, magical, Drow, etc.) will only be able to attack every other round. Even if a player has multiple heavy crossbow tokens, the cumbersome nature of this weapon–changing from heavy crossbow to heavy crossbow–will still incur a combat round penalty.