Who fights whom? Humans or dwarves?

They will definitely start training horses in the second month, which means there will be three times more of them than our dragons, so the odds are not equal. Against humans, preparation is definitely needed, and a bit of luck wouldn't hurt either. Although, there is a possibility to use Battle Mages, but that won't work with horses – they destroy units in stacks, and resurrecting 40% of the killed units isn't enough to defeat them, except maybe for Jarls and Draconians. That's where pyromancy would be useful.

Added 2 minutes later
And everyone has forgotten about Divine Retribution – oh, how it will cut down the paladins, dealing 15-20 damage to paladins for each killed stack. How did I not think of that before?