Re: 2nd question
'So, ignoring the fact that the earth and the sun are linked via gravity cos they're relatively close, and so this probably doesn't apply, '
Struggling with the general assumption on the thread that bodies and matter will be static relative to each other due to gravity. The theoretical and physical discovery of gravity waves says this is not the case. Gravity bound bodies move apart and together due to fluctuations in spacetime.
As I understand it, this includes the subatomic particles as well. This being the case, a Hubble constant applies to all physical matter as it is underpinned by, and exists within spacetime.