As the title says,
I’m a human but I like the asura’s home instance a lot more.
Is it possible to change home instance?
You can go to any of the home instances on any character. If you want, you can avoid the human one forever (outside of personal story steps).
And if I buy a node, will it be available on all home instances?
Yes, anything you unlock for your home instance will appear in all racial home instances.