I'd say he should worry about meeting new potential partners and finding a spark with one before he worries much about the rest. It's only when a potential partner is actually showing interest that any of it matters.
Then it's time to point out that he's polyamorous. It doesn't seem to really matter whether he mentions that he's married or poly first, as long as he's honest about his interest and honest about his situation rather early in interactions. Not that he should dump that on somebody before they're even convinced that they're interested in getting to know him better; it's a balancing act to avoid scaring somebody off prior to them getting strongly interested and leading them on for a length of time without fully informing them.
When speaking of various forms of non-monogamy...it ain't poly if you're just fucking around.
While polyamory, open relationships, and swinging are all distinctly different approaches to non-monogamy, they are not mutually exlusive. Folks can, and some do, engage in more than one of them at a time--and it's all good.