MonkeezOnFire
Adventurer
Reading through the first chapter I think I would get rid of the contrivance of the Flaming Fist pressing the PCs into service. Instead, I would have them specifically hired to track down Kreeg, who is rumored to not only be in Baldur's Gate but mixed up with Dead Three cultists. Their only clue is a not-to-be-trusted former pirate in the Elfsong Tavern.
There are some hooks in the Baldur's Gate Gazeteer section that relate directly to the adventure. Hamhocks Slaughterhouse has been taken over by members of the Cult of the Dead Three so investigating there could lead the PCs to the bath house.
Alternatively, a cambion named Kaddrus is mentioned in the Hhune house entry that is investigating the disappearance of the Shielf of the Hidden Lord. Mixing in some hooks there could lead the PCs to go on an investigation that then leads them directly to Vanthampur Villa where the shield is being kept.
Both definitely require some fleshing out and creating new content to work. But I like that the option is there to make the initial city parts more of a sandbox.