Ask for the same terms as the founders, and ask for a big enough stake that you have something left after a prospective Series B round assuming 20-25% watering

Ask for the same terms as the founders, and ask for a big enough stake that you have something left after a prospective Series B round assuming 20-25% watering down in each round. That makes it so that the founders have to do to themselves what they do to you so your interests are aligned.