I'm playing with this mod for the first time. I accepted Sir Havum's quest to kill the dragon in Umar Hills, and have just killed the dragon.

I do not want to take the "new route" to get to spellhold. My plan is to let my ole buddy Saemon take me (I've read that the new way can sometimes be buggy). Anyhow, before I reported news of the dragon's death to Havum in the Order of the Radiant Heart building, I visited Gaelan Bayle and paid my 15k gold to enlist the aid of the Shadow Thieves in finding Imoen. As normal, the game advanced to chapter 3 and I saw the usual cutscene.

Next I went to the Radiant Heart building and offered news of my victory over the dragon. I received a nice xp award and an offer to perform another quest (kill vampires). I went ahead and said yes, unsure of what consequences this might invoke. When I did, the Chapter 3 cutscene played again (the one that shows what's going on with Irenicus and Imoen over in Spellhold).

Clearly something is whacky here, so my question to those who might have seen this before is, can I just keep playing, or should I reload and tell Havum that I am not interested in any further quests?

My party (from a RP perspective) has no problem helping the order out. But my concern is that something might break in my game, which I don't want.

Anyone seen this before and/or know how I should best proceed? I did save right before talking to Havum by the way, so I'm covered in that respect.

I did try Saerileth a while back and also killed the dragon. In my case, however, I wasn't powerful enough before Spellhold, so I killed it in Chapter 6 (when I did most of the quests).

IIRC, the Paladin offers to assist you at Bodhi's lair, which could cause problems (especially from the ominous replaying of the Chapter 3 cutscene). To be honest, I'd reload the save, take the XP reward and decline to go against the vampires. 'Tis the safest course.

Agreed, that's what I ended up doing. I tried this a couple of different ways, and during one of the cutscenes I noticed that there were actually 2 Irenicuses in Spellhold, and he was interupting his own dialogues. It was just too much whackiness to consider going forward. So I got my xp, and told Havum that I just wasn't comfortable with his proposal to go against vampires.