OK After you rescue Nalia from Isea, is there any more sub-plot stories around her? (I'm a fighter so her Keep is my Stronghold) or is it safe to get rid of her?

Cernd, has his child and returned to grove. Any other stories with him? If not, I'll leave him in the grove.

Which chars. are worth brining into the party for their sub-stories. Currently I have Jaheria, Amomen, Minsc, Arie & Nalia

Thank you

Minsc doesn't have any quests. Jaheira has a long, complex quest if you play as a male, but I don't know how much of it shows up if you're playing a female PC. Edwin has a humorous quest, which you could do along with Korgan's. Aerie doesn't have much unless she's a love interest. Viconia? Don't know. Mazzy has a brief quest. Valygar must be with you if you want to get into the planar sphere, but I had him in my party for two weeks of game time and never found another use for him (god knows he's no fighter). There is a sort of quest involving Yoshimo, and if you dont' know what I'm talking about, you won't hear it from me. Keldorn and Jan have minor quests. Anomen's quest is elaborate, and turns him into an excellent NPC if you play the good options. Haer Dalis has a quest but you can get it without him (and he's useless, so don't bother). Hmm. Who am I forgetting? I think that's it, since you already mentioned Nalia and Cernd.

This is a spoiler involving Haer Dalis and Aerie.
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Well...if you are having Haer Dalis and Aerie in your party, with the later being your love interest, a triangle relationship will evolve. Haer Dalis will then challenge you to a death match.(that "Drizzt wannabe" really got the balls don't he)

Dalis is worthless, and you never get to duel with him. At some point he tells you to break it off with Aerie. If you say no, he gets a bit annoyed, and after a while challenges you. If you accept, Aerie breaks it off with you. If you try to talk him out of it, he won't have a bar of it, and Aerie breaks it off with him instead. Gah, Aerie is such an annoying goodie-goodie.

But is there anymore subplots with Nalia after you rescue her from Isea's clutches or does her story basically end?

No, that's it.