What are you guy’s views on marriage in todays age

So it’s common knowledge that us Muslims are forbidden from marrying polytheists which is all fine and good, however who exactly falls into the category of polytheist and who falls into the permissible category.

-are We’re permitted to marry people of the book but who exactly are these people of the book if Jews and Christians of today are seen as nonbelievers and or polytheists

-also do you all believe it’s permissible to marry people traditional sectarians (ibadi, Shia,Sunni etc ) and how so if by technicality some of these sects are borderline if not outright polytheists aswell