I did indeed completely forget to write the starting setup (which should be that the king starts in your left hand corner camp, surrounded by three footmen). I'll update the rules soon/tomorrow. One can introduce pieces to the camp that is nearest to any fortress you occupy.
It could theoretically work with four players, but I think it'd need significantly cut down rules and a slightly changed board perhaps as the current one doesn't actually have fourfold symmetry. Might be worth trying though.
I will indeed write better explanations of the moves etc when I get time.
As for stalemate, I think I need to play a few games to work out what the right answer is there. Regicide means that the player cannot be defeated by capturing their king, only by being wiped out or defeated by territorial control. I don't know whether that would make a vast difference because I'm not sure what the more common form of victory would be.