Lemmy and Kbin are very similar, it’s reasonable to be confused. Very important, Lemmy instances and Kbin instances can interact with each other’s content, so whatever your choice ends up being won’t be about content since they have effectively the same content.

The difference between the two lies in some behavior differences (for instance, Lemmy intentionally doesn’t have a karma system, and Kbin does), in their very different web UXs, and since their APIs are different, the native apps talking to each are also different apps.

There’s also an ideological aspect, the creators of Lemmy initially created it because they were finding Reddit content to be too US-centric. Some say that they support communist dictatorships, but I’ve looked a bit, and evidence of that is flimsy, it looks more like they decided not to suppress anti-American content on their instance, and people may have extrapolated a bit. Or maybe there is truth to the rumor and it’s just well-hidden? 🤔 I believe the creator of Kbin started it because he disagreed with what he understood as the ideology of Lemmy’s creators.

I’m on Lemmy because it and its apps are more mature, and I’m not convinced by karma systems and what they may incentivize. And because I don’t find the case for the creators being extremists to be very convincing, from what I’ve seen. But Kbin looks pretty decent too.

I’m afraid I don’t don’t have answers to your other questions, but I thought I’d inform on this.