no
Yes.
In order to marry anyone you first need the Amulet of Mara. You can acquire this amulet from Maramal at the Bee and Barb in Riften.
Usually, to get married in Skyrim, you will need to do a quest for the person you are trying to marry.
No you can't
Isnt nocturnal a daedra? if so then i doubt it
No, there is a limited selection of people you can marry, you can only choose from amongst those.
Ysolda because she will end up being an asset to you
You can marry the person, then divorce that person, then marry that person again.
No
NO, Aphrodite had many other lovers but didn't marry but once
Yes, he married twice.