Montresor drinks to Fortunato's long life which he later ends.
I took from their sconces to flambeaux, and giving one to Fortunato, bowed him through several suites of rooms...
The dark and eerie catacombs symbolize Montresor's dark and eerie persona.
It foreshadows that Fortunato will not die of a cough. Montresor says true because he knows how Fortunato will die. He will be killed by Montresor.
There were no attendants at home; they had absconded to make merry in honor of the time. I had told them that I should not return until the morning, and had given them explicit orders not to stir from the house. These orders were sufficient, I well knew, to insure their immediate disappearance, one and all, as soon as my back was turned.
Montresor is the protagonist. We don't know what Fortunato thinks, but we know what Montresor thinks, so he is the main character, or protagonist.
Fortunato is the antagonist because he insults Montresor, so Montresor decides to get revenge.
Montresor tells his servants that he won't be back until morning and not to leave house the house, so he knows that they will not stay at the house because no one will be able to stop them from leaving.