Personally I'd prefer to stick to the original concept of having two kingdoms that are at war with each other. 
My take on things would be the Beorc kingdoms wanting to invade one another, and making preparations to do so.
But seeing as how there's a Laguz area inbetween they'd probably want to get the locals on their side to secure a supply route. Most Laguz tribes though probably wouldn't appreciate Beorcs waging war against one another in their lands, so they'll be fighting to keep the invaders out, or negotiating something in exchange. 

I guess you could say this is North vs South with Laguz getting literally caught up in the middle.

My issue with 'Beorc v Laguz' or Laguz being used as refugee's is that I can't imagine Beorc policy being overly accepting of taking in Laguz. The concept of having a few sneak in; perhaps even establishing their own secretive little community out on the streets is neat. But as an overall focus for the roleplay, I find it a bit of a stretch to think Laguz would flee persecution from their kin (even if they're savages), and rely on humans who persecute and disdain them. 

Either way, having the Laguz pitted against the Beorc sounds like it'd detract from the entire point of having Laguz as a race in my opinion.
If we want to incorporate Laguz taking back their lands and some major Beorc v Laguz conflict, you could easily have the Beorc's invading and claiming land with the intention of invading the other Beorc nation. In that sense the Laguz would be a petty threat, and easily brushed aside at first. But war is a tricky thing, and something might happen to make the Laguz more dangerous later on, whether that be unity, magic or some sort of alternate intervention.

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As for Chapters, I think that's compulsory component of any group roleplay that's intended to last longer than a short story. It actually fits in pretty well with the base material, but more importantly an introductory paragraph makes sure characters know what's going on, and what's expected of them. People can obviously deviate a bit and be creative of course. But setting out the central premise and objectives helps keep things orderly and manageable. Having people go off on a completely random tangent sucks.

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Available classes should probably be listed so we get variety.
I might even go as far as suggesting you specifically create positions for characters to fill xD