Obviously, over the decades, there have been lots of first meetings between different heroes. Do you have particular favorites? Are their any heroes you think should work independently for a while before meeting any other heroes?
I'm fond of Batman and Superman not meeting until there is a Robin. I'm particularly opposed to all the Superboy scenarios where he meets various young heroes before they are heroes. Though I did enjoy some of the stories (Hal's particularly).
I think first we saw of Batman and Superman knowing each other is that they already know each other when on JSA. Similar happens when Green Lantern and The Flash (Hal and Barry meet), as I recall. Is Starro (with Justice League already formed) the first time we see that Barry, Hal, or J'onn know any of the other heroes?
Are there any heroes that you think should meet one-on-one before meeting on teams? I'm a go for Atom and Hawkman (pre-Hawkworld version).
I find Ollie and Bruce well suited to coincidentally meeting somewhere as Bruce and Ollie and then events requiring the costumes to come out.
I have an affinity for Superman immediately trying to meet Wonder Woman, curious as it if she is somehow another surviving Kryptonian, but that may be a bit silly.
Ralph and Barry are a must to meet privately first. And I like Cissie and Bart's first meeting a lot, too.
Then, of course, there's the issue of when they should find out each other's identities. Who should learn each other's identities early v. late? Who has one-sided versions where A knows B's identity but B doesn't know A's? Who should absolutely never learn the other's identity? One issue with the last is the sprawling "families" - Batman may have no desire to tell Gar Logan his identity, but Gar knowing Robin's mean he knows Batman's, etc.