How would you describe the solid foundations of a relationship ready to enter into ENM?

What questions/scenarios/topics of discussion do you recommend we cover before starting?

What are the common missteps and failings you notice with new people?

For context. We are a married couple. HS sweethearts, so each others first and only up until very recently. We maybe dove a little to fast into swinging. Feel free to stalk my post history for the full story if you have the time. We’ve since stepped back and refocused on our relationship and building more intamacy/connection again. As I continue to process some jealousy/insecurity/fear of abandonment that I didn’t expect to come up for me. I felt as though we had a very solid relationship. But it seems these things tend to place a magnifying glass on it and can find even the smallest of cracks… resetting and preparing for a new start when it feels right.