@ Bounty Hunter: So I've been looking through Defenders of the Faith and other books. There are several prestige classes that give some interesting flavor for a good story hook.
1. Consecrated Harrier - A holy bounty hunter, the consecrated harrier is assigned a mark for some egregious offense against your church. Doesn't have to be related to this adventure. Maybe you're just hitching a ride, so you serve on the crew in the meantime while you travel from port to port, or maybe you got a hit on a location, and you're headed to Waterdeep to look. Whatever, but they're going to be mobile. The character doesn't get many spells in these levels, but gains bonuses in many social skills, detection, and stealth.
2. Holy Liberator - Just what it sounds like, they fight tyranny, slavery, powerful evil. The moderate qualifications for the class means you could have two levels presently. They don't gain much in magic power, but are great for non-holy character classes to add positive energy powers to their character. A cleric would add some abilities that Paladins have, which would be a different sort of holy warrior without feeling the need to be lawful stupid. Chaotic good clerics are often drawn to the class.
3. Hunter of the Dead - Hates undead, hunts undead, gets really good at it. Enough said. At your present levels, you could gain two levels as a cleric base class. Doesn't really gain much additional spell ability.
4. Sacred Exorcist - Same idea as Hunter of the Dead, but adds hunting/dispatching outsiders to their bag of tricks. You have to be exemplary in your faith and devotion, morality, and be sponsored by a specific church. Sacred Exorcists continue to advance in spellcasting as normal.
5. A great Faerun-style class is Morninglord of Lathandar from Player's Guide to Faerun. They get most of the goodies that a cleric archtypically gets, but some additional specified coolness in the form of powers related to Lathandar, such as light abilities and greater turning power. It's fairly easy to qualify for, too, which would allow you to have four levels in it at 9th level, while still casting spells as a 9th level divine spellcaster and spells per day as a 9th level divine spellcaster. Very mobile, expeditionary priesthood to spread the news of their god, Lathandar. Can be any good, which could work better in this adventure than a LG character. A ship hunting pirates could present some challenges that would really test the rigid alignment view of Paladins and other LG characters, as a lot of stuff may be happening outside of the law to hunt and destroy piracy.
Or, you can stick to a vanilla cleric, which believe me is no pushover. I played one in a different Forgotten Realms PBP adventure, and had a blast. Would have smashed the end villain, too, saved the day, had I swung first on initiative because he had been sufficiently weakened (largely by me). But he got me...we won't go into what specifically happened, but it didn't end well for the party.