Are there any NPCs that need to be kept with your character on a regular basis, for storyline purposes? I'm on my first run through the game and am not sure who to drop/keep when I pick up new NPCs. For example, Kreia seems kind of important - should I have her in my party all the time (bit like Bastila in KOTOR I)? I'm playing a female lightside sentinel, does this mean I don't need Visas? Or does she have a story that could prove important? I'm less concerned with "party fit" than I am with storyline fit.
Also, are there specific NPC quests per planet (eg Mission-Tattoine in KOTOR I) or can I safely mix and match without fear of missing out on an important plotline?
Any help would be welcomed.