You may also want to do a search (Advanced search feature or Tag search) for the word "boundary" and/or "boundaries." Many polyfolk prefer to agree on boundaries which can be more flexible or personal to oneself, rather than having rules to follow "or else." So there are lots of juicy discussions here, which center on the concept of establishing boundaries, that may give you good ideas.
Also, I do think that is more reasonable to agree to rules or boundaries for yourself and your husband, and let your additional partners know what those rules are so they can choose whether or not they can live with them. But it is a bit harder to make rules for other people who are not part of your dyad. Also remember that most people will have their own rules or boundaries - so be prepared to ask yourself whether you can abide by theirs, not just that they have to abide by yours.
The world opens up... when you do.
Oh, oh, can't you see? Love is the drug for me. ~Bryan Ferry
"Love is that condition in which another person's happiness is essential to your own." ~Robert Heinlein