After playing SoZ, I say no more races and classes. We have enough that even after changing the party limit to six, I still couldn't create all the combos I wanted. Instead focus those resources enriching the content we already have. Each race needs more heads, we need more hairstyles, more armor models, more weapon models(like an actual flail). Rapiers need their own combat animations, etc.
After that I say set the XP in Maztica. You're a major part of an Amnish colony freshly established and you play a major part in its development. Migrate the trading mechanics from SoZ over to this but basically make it a big combo of Crossroad keep and the trading company. You can establish trade with other colonies and native villages, but trading with some will cause others to deny you and who you establish relations with determines who you can recruit and what you can build in your colony.
The story could lead up to when the spellplague hits and Maztica is transferred to Abeir.