Well, in my experience the relationships come before the decision to be polyamorous. I knew my fiancee was bisexual and maintained a loving friendship with the girl she basically grew up with and it wasn't going to end with our relationship starting. So I had to decide to accept it and work out the jealousy and insecurity I denied having. It took a long time and wasn't easy but loving her for who she is is the most important thing.
In your case, I imagine you want to make as many friendships as you can and if something happens you'll be emotionally prepared for it.