Sounds like an interesting and intriguing concept, I wish you success in bringing it to life.
Advice on a couple things which stood out to me:
All the same it can be sold to a noble collector in Athkatla but the real story begins if it is kept and worn.....
This sounds like it would be easy for a player to skip the quest altogether (perhaps unknowingly) by selling the item. I'd consider adding a plot line to lead the player back towards the amulet after selling it, so the quest can still be started in another way. For example, maybe after a few days the party catches a rumour of the noble collector dying under mysterious circumstances and is called upon to investigate (or maybe they're even suspects in his death now). Or the noble's behavior changes because he's affected by the artifact, and one of his close friends/family comes to the party with questions or plea for aid.
and if you refuse his attempts to 'save' you which involves him joining the party and trying to destroy the amulet without killing you
I'd recommend not making the extra companion mandatory for completing a quest arc. With the amount of NPC mods out there now, those party slots are very precious and by requiring one of them you risk losing a significant part of the audience who'd prefer to have their own NPC party selection. Perhaps the paladin offers to help, and then if the player accepts he also offers to join the group. If this second offer is refused, he can still try to help (perhaps staying at one of the inns, if multiple interactions with him are planned) without joining the party.