It’s using an engine that is purpose built for the task, so I don’t think it will have the same kinds of issues. Perhaps some brand new FUN ones though!
I believe one way it gets around at least one of the kraken sources is by always having either your vessel or your point of view at the center of the “universe”, and having everything else move around that. That way the floating point precision isn’t really a problem, as the things that are far enough away aren’t likely to be simulated to the point where the errors would have an effect. Could be wrong about this though.
No. The OS license comes with the hardware that is bought. If your hardware supports the OS, you get the updates for free. There is no subscription needed to keep a Mac up to date.