First, do not do it!
Second, took my wife and I in Saigon 6 months 8 days to get legal marriage documents this year.
Third, Yes we had to pay bribe money
Fourth, They are changing visa requirement this next 2 months from a 3 month visa to a one year visa multi entry.
Fifth, Beware of local district police where you will live, you must register with them too and pay them.
Sixth, Beware of family ties. She and her family now own 50% of everything you have.
Seventh, Do not put her name on your bank account or credit cards.
Eight, Pre Nupts are not allowed by Vietnam Law