Is it illegal to do more than one kick between arm strokes?
Not if it's a dolphin kick. I'm pretty sure you could dolphin kick an entire fly race without ever taking a single arm pull and be legal (as long as you surfaced before the 15m mark off each wall).
I've always been intrigued by those people who do extreme long distance butterfly, like Vicky Keith. (Not that I'm ever planning to try something like that, I'm just amazed that it can be done!) Has anyone ever seen someone doing that, or know of an online video clip? Is the stroke done somewhat differently to be able to last so long?
There used to be an online club called the Butternuts, for people who had done at least 500 continuous meters of 'fly. I tried to find it yesterday and just got a whole bunch of horticultural sites about walnut trees.