So in the space of the 3 hours we ran this (it went slightly over, but not by too much), we settled in, talked about characters and sort of had the whole scene where the Handmaidens explained the situation to the PCs.
Once they determined to go through with it, they stepped through a teleportation portal which linked to one of Orcus' planar ships- a vessel called the Shevaithan.
The Shevaithan is the third of three ships in Orcus' fleet that are able to actually travel across (and through) the Abyss.. It is crewed by abyssal ghouls, commanded by a rotfiend captain (Captain Xur, and we determined that Xur and Koramus had served together in a previous conflict, where Xur was killed, so she especially hated him). The other thing was there are Nycadaemons aboard the ship- 3 on deck when the players arrive.
The adventure module comes with a deck-plan map of the ship shown above. So in the battle- it's hard to describe- this was a first time for epic level gaming for all of us, but it wasn't unmanageable at all.
The players stepped out of the teleportation circle and were immediately jumped by the Nycadaemons- the warforged wizard ended up kinda on the outside and got pounded on pretty good- the Nycadaemons have a wicked axe attack that does a pretty good chunk of damage. Legend was bloodied just in the first round of combat, but quickly teleported away, leaving behind storm pillars that deterred pursuit.
The rest of the group was swarmed with ghouls- they were dealing out a ton of necrotic damage, plus immobilize effects. This had the effect of keeping the group kinda locked down by their point of origin... the warlock teleported out as well, in another direction but remained immobile. He cursed everything he could see...
The rotfiend captain relied on psychic powers- one of which diseased Koramus with abscesses for a while.
Soon it came down to the cleric who managed to wipe out the ghouls pretty quickly (within 2 or 3 rounds).. but the captain and the Nycadaemons turned out to be fairly hardy: The Nycadaemons were resistant to radiant damage (and cold), and Captain Xur had similar resistances plus resistant to fire.
This really weakened the cleric against them. Koramus and Moonstone (surprisingly hardy and unhittable) held the Nycadaemon off while Tyvraxus concentrated fire- his fire powers are not affected by resistance because they come straight from hell.
Xur herself had the power to create a zone of miasma that did psychic damage, and she maintained that over the PCs to slowly drain them, while she also fought off the cleric (they could both fly, so they clashed above the forecastle a few times).
At one point Legend used deceptive shadows on Captain Xur and that kept her isolated against just Clarity for a few rounds.
So.. long story short, they ended the battle (and the players learned most of their powers). So that was a good intro to the adventure.
Afterwards, the players took a short rest and attempted to seize control of the ship- it was still moored far below- to a place called the Red Hold. The next step would be to journey down the abyssal anchor-chain and free the Shevaithan from it's moorings. They also discovered a note that mentioned Orcus' Castellan (Harthoon) and discovered crates of black rock that Legend identified as chunks of Timesus. They also found the ship's treasure of platinum near the command center of the vessel. Tyvraxus took Captain Xur's pirate hat.
As the group started to make plans about journeying to the Red Hold (either via flight, climbing the chain, or bringing the whole ship down..) the hatches burst open and a fresh wave of abyssal ghouls, nycadamons and a pair of leaders spilled out.
One of the leaders was a Larva Warlord, and the players had a hard time pinning him down- he had a ton of hit points and was sort of like a boiling swarm of insectoids and beetles.. the swarm druid locked him up in combat and or a while it was like a tornado of battling beetles (her blue and purple beetles against the abyssal red and black) battling on the forecastle.
So that was pretty cool. There was another battle. This one seemed to go quicker as people had a better sense of their powers.
We ended, did an XP divvy and made plans for next session.