This is a very important point, careful use of GCs for a special subset of allocations that say have tricky lifetimes for some reason and aren't performance critical could have a much smaller impact on overall application performance than people might otherwise expect.
Yeah, and it's even better if you have a GC where you can control when the collection phase happens.
E.g. in a game you can force collection to run between frames, potentially even picking which frames it runs on based on how much time you have. I don't know if that's a good strategy, but it's an example of the type of thing you can do.
It's a string in a well specified string format. That's typically what you want for serialization.
Temporal is typed; but its serialization helpers aren't, because there's no single way to talk about types across serialization. That's functionality a serialization library may choose to provide, but can't really be designed into the language.