The size of the characters is not limited, so no restriction. But you'll have a lot more info this weekend, as I'm adding some stuff to the character editor right now.
And about character editing, maybe we can start working on something now: the palette issue. As the game runs in 8bit screen mode, and I made my palette in a hurry, it would be better to start with a better one. So if some people could send me their palette, or pictures with thair character's colours, that would be great.
I will open a topic this weekend, so as soon as the palette is ready, I'll update the pak files, and everyone would be able to start making characters.