A while back, I asked for some tips on making a D&D campaign, mostly with worldbuilding, and I got some helpful responses with good resources. Now, I'm trying to think of a way to expand it. Originally, I was thinking of the players deposing the local Big Bad around level of 7 or 8, and they'd be at the island setting because of shipwreck. Now I'm thinking of changing things up a little to give players some choices in the matter, since some players/characters resist Closed Circle scenarios (and I don't blame them). I'm trying to think of a way to get some level 1 characters steadily built up until plot hooks lead 'em to the island. Also got some miscellaneous stuff I could use some help in brainstorming.
The lay of the world: There are two major continents involved. The eastern one's essentially Europe, and the western one is Africa-like. They're technologically on par with each other, mostly. The islands in the original scope are in the middle between them, slightly north of the equator. They used to be used as a stopping point for inter-continental travel, but unusual incidents have gotten them a reputation for being cursed. Sailing technology developed enough that they could be safely passed by.
The islands themselves: Concept is a vague mix of Japan and Hawaii. They're very backwater, and still working on a way to produce reliable steel. When they did have contact, they tended to gather steel by gift exchanges with sailors. Magically, they're distinct from the rest of the world. Instead of arcane magic (genetic mental block), divine magic (no deities they worship), or psionics (means of developing it tightly controlled), they have magic with the elemental "power source" from animistic elemental spirits. When I was working in 3.5, I was using the Shugenja class. I'm retooling other classes appropriately.
Hook concept 1: One of the islanders barely manages to make it to the eastern continent and tries to find some adventurers to help him out. He ends up having to perform in a circus for the sake of room and board, showing off his brand of magic and performing some fake fortunetelling. The ringleader doesn't want to let him go.
Post-adventure: The islanders will be pretty much willing to let the PCs take over ruling the islands, expecting them to do a kinder job than the tyrant. I suppose his underlings could potentially survive to cause problems. There's economic opportunity as a tourist location as well as the pearls the islanders have gotten good at farming for magic and currency purposes (they sometimes use 'tile' seeded pearls as currency). Of course, if the PCs aren't the type to take over, they'll settle for showering them with gifts, which will include three giant sacred pearls I haven't settled on properties for, yet.
Suggestions for handling aquatic combat: The islanders have a natural swim speed, so some of the evil ones will try to claim that as a terrain advantage.
General suggestions for the build up will be appreciated. I have limited DM experience, and level 1 would probably be simpler to start from.
Just kind of throwing this out, so any random ideas would be appreciated.