Merge in what way? In terms of user interaction, they already are merged. Lemmy users can comment and make threads in kbin communities and vice versa.
And in terms of underlying codebase, there isn't anything to merge. Lemmy and kbin are written in two very different programming languages. Trying to unify them would mean huge amounts of effort for no tangible gain.
Default settings probably will get changed to something more sensible, but might still be a while till it makes it to the server.
Fwiw Lemmy is written in Rust
The reputations system is still a bit messed up and still works like in th earlier days when upvotes were actually boosts. It's probably gonna get changed eventually.
Not just likes. Any post a user from another instances sees from you, is also stored on their instance. But I don't think it's stored indefinitely and it's also not stored in a way you can make use of. So if the server your account is stored on explodes, technically there are still a lot of your posts stored all over the fediverse's servers, but there's no feature that would allow you as the (former) account owner to ask for them or easily collect them.
You can download your data/posts and move to another instance, but you can not upload your posts to that instance, you can import who you follow and blocklists I think and your followers get migrated automatically.
This one's already reported and ernest has responded to it though. If things go well he'll br able to start looking at pull requests today. Doing any fixes beyond that would probably come after that.
Use the app as you would want to use it normally and if you encounter any errors, weird behaviours or oddities, report them to the place they are supposed to be reported to in a descriptive way and answer any follow up questions.
Most magazines that come from other services are auto-created by "ernest" I think
It's on the way
https://codeberg.org/Kbin/kbin-core/pulls/154