@FanOfMostEverything  
I’ve worked it out a few times and, while it can get hairy in the way they would target abilities together, I don’t think in the end there is any way to push it beyond just a plain “Instead of getting one copy of an activated ability you get two.” Eventually you have to go back to a copy of Crusaders’ Banner’s ability that needs an ability you have activated, and you’ve only activated two abilities (one for the original trigger and the Strionic). That’s just one copy of each, though…

Yeah, Literally as I got on fimfiction to take a look at the rest of them I realized I messed up.

@digiman619  
The key word here is “trigger.” As you astutely noted, the Banner has a triggered ability rather than an activated ability, so it won’t trigger itself. (That said, it can get pretty nuts with a Strionic Resonator, which has an activated ability that copies triggered ones, though still not infinite.)

You do realize that if you have two of them they will trigger off each other, right? It might even trigger off of itself…