I have a small site and spent an unreasonably long time weighing in between

- host my fonts and therefore if something does not work, nothing iwll work (whihc is a consistent user experience)

- or source from Google directly but if Google goes down or the user somehow filters Google, the experience will be awful

I chose to use the Google way - not only are they much better than I am in everything, but the user may miraculously have the font cached, a small bonus

no, assets are siloed by domain to prevent tracking, so the user will never have the font cached. I say just mirror it, if your site is down, it's down anyway, and the user will have to connect to one less domain. If you have any images at all on your site, the font is basically just the size of one more small image.

You are dismissing the obvious, default natural option of not specifying a font and letting your visitors pick the one that suit them best.