Similar situation here. It started out out with friends of my wife and I. It was suppose to be more of a friends with benefits type relationship, but it went full poly very quickly.
We are figuring out things as we go. So far, we have managed to work past many issues. The main advise I have been going off of are
1) Communication. So many forms of this, but it helps to keep this up and keep everyone talking.
2) Don't mediate other people's fight. This has not been an issue yet, but it was an issue in a previous triad I was in. Basically is two people are arguing, we can be a sympathetic ear, but we are not to really try to fix the argument.
3) Feel free to state feelings. It does not mean anything has to change. But we should feel free to say what makes us comfortable or when we feel jealousy.
4) Work off of boundaries and not hard and fast rules. Basically realize that we are all opening and changing. So rules are more flexible.
5) Make sure people get enough sleep. This one may be more specific to us, but lack of sleep makes people grouchy and easily irritated.
6) Have fun. This should be fun and happy.