re:Isn't there also that tradition where the bride and groom hold hands and the vicar/priest/whatever ties a wide (purple) ribbon around their joined hands and forearms?

its not a ribbon, but a strip of cloth, (don't know the color) and its part of a catholic wedding mass- and maybe others.

Jumping over the broom, i have heard comes for Ashanti customs. most slaves, where held not to be "real" people, so even if instructed in christian believes, they were exempted from (christian and or legal) marriage.

but since people everywhere mark marriage, they devised their own customs.