Who says Gul'Dan will even find Azog in battle. Azog gets in combat situations while Gul'Dan hands to the back. That doesn't mean they'd stop fighting. Bolg is still there but don't you worry. Azog won't die but Gul'Dan will.
There are quite a bunch and they also have a staggering numerical advantage along with superior battle tactics.
Nah. They lost a lot of ogres against the pitiful alliance forces at the end of the film.