i ended up doing the mod in chapter 2 cause I still needed some extra coin for Gaelan B (I'm running SCSII with the increased price asked by GB). Overall an excellent mod. The art work for the levels was especially good. I think I would have liked a little more licentious activity from Castor especially in regard to the female NPCs (course, Castor is my favorite from the comic so I'm probably biased).
You can certainly wait until Chapter 6, sure thing.
I'm sorry to say we don't have an Imoen reaction for Castor, though. We've got one for Viconia/Nalia/Mazzy/PC/Jaheira/Aerie, but as for Imoen, it's the same as it is in the original game: she won't interject.
Is this meant to be done in chapter two? Or can you wait till chapter six after you return from the Underdark? I think I prefer chapter six if only because Imoen would be in the party then. I mean if Castor is hitting on all female NPCs, the Imoen encounter ought to be one of the better ones. Also, I'm ussually a bit streesed by thetime the underdark bit is done.... Dungeon Crawl sounds like it'd be a nice break just about then.