1) Scholars have ruled that temporary marriage with them is permissible, but most have said that permanent marriage is not permissible. A number of Maraje’ today state that it is permissible to marry them permanently, but historically most have said it’s not permissible.
2) As for a Muslim woman marrying a non-Muslim man, it is not permissible.
3) They can marry a Jewish or Christian woman on a temporary basis according to all scholars. As for temporary marriage, some Maraje’ allow it while others don’t. Ayatollah Sistani says permanent marriage with them is not allowed based on obligatory precaution.