The PCs should be 2nd level when the first combat encounter of the adventure occurs. The first wave consists of three guards mounted on warhorses. The second wave consists of a half-ogre and four more guards on foot. There are also random battlefield effects, some of which can cause damage (like the volley of arrows), to represent the larger battle.
In the wilderness exploration section, when the PCs are 6th or 7th level, they can explore Bluemaw Cave. They'll fight seven gricks initially. Later, they'll come across a sivak draconian with five baaz draconians. If they get into a fight with the draconians, a grick alpha and two regular gricks join the fight, although they will attack the draconians as well as the PCs.
In the City of Lost Names, there's an occupied mansion. The PCs are expected to be 8th level when they explore it. There are four kapak draconians standing guard outside. Once per hour, a patrol of eight Dragon Army soldiers checks in. Inside, there are a total of four kapak draconians, two bozak draconians, a wasteland dragonnel, fourteen Dragon Army soldiers, a hobgoblin captain, and an aurak draconian.
The final battle is against Kansaldi Fire-Eyes (CR 11) and a Huge-sized young red dragon (CR 10). The PCs are level 10 by this point, but they'll have also just gone through all the encounters in the Flying Citadel and won't have had a chance to rest yet, so they'll hopefully be pretty beat up at this point.