I manage a low volume website, but with good SERP position. So far I have only a few reviews in Google My Business (GMB).

My primary question is, does Google use the reviews/stars from GMB in the SERPs or only if I supply it in the microdata?

If I have to use microdata, do I need a user review process separate from GMB? Everything I read says I shouldn't copy reviews from other sources and that they need to be unique to my site.

As a secondary but related question: Per Google guidelines, we aren't supposed to have reviews on our home page, only leaf pages. This implies that the reviews should be product reviews versus company reviews. My site advertises a service, and it doesn't make sense to create product reviews at the leaf level. So, pulling GMB reviews makes more sense IMO.

I'd appreciate any clarification on this anyone can provide.

Thank you.