It's certainly possible that some factions of the priesthood of Ioun could have hired a killer at some point, the priesthood of Ioun isn't what one would call organized religion, the libaries are, dewey decimal and all that, but the priesthood not so much.
Ok, suggestions, take them leave them, Don't want anyone to feel like I'm telling you what you have to do with your character.
Kyriel and Sharun could have been asked by another priest somewhere else if they would look over the pilgrams here in Wellspring as there will be many people and no priest is currently assigned to this temple.
Bearn could have come to Wellspring to bring his clanmate a message of some sort,
Gurk could just wander into town with no real plan except maybe buy supplies and good ale in the tavern
Phaeryn I got nothing,
Baden could be here to resupply and hopes of finding a new job.
And of course Barek already lives here, and being a dwarf I don't need an excuse for placing him in route to the tavern.