I / we have been in this a long, long time - 20+ years of cheating and infidelity to start, 22 years of doing the hot wife thing. Respecting your privacy, given the lack of more context:
Your basic instinct seems sound; first and foremost, it's all about her - not him, not you. As a secondary consideration, it's about her relationship to you, and yours with her. You both have to find a voice to immediately boot any third party who isn't in line with that.
We used to have rules, many rules. In perfect 20/20 hindsight, most of 'em were mine, stupid ...... for the most part, like no kissing, because it upset me. I didn't (then) take the time to find insight that she might need that.
This lifestyle is a lot of work. There are no easy ways to recruit encounter partners, figure out who to trust, no magic to any of it, other than grinding through it. As you gain experience, confidence, and inner voice, it gets easier, but it's never easy.