I've lived in Vietnam on and off for several months at a time. One of the safest countries anywhere ( as long as you don't badmouth the government)

Easy to live on sub 700$ a month if you're happy with air conditioned studio, mostly asian food, scooter and not going to high end bars.

Get the 1 bedroom apartment, quite often takeaway/delivered western food sub 1500$ a month.

Go eat out western food everyday, live in a 3 bedroom in the nicest district go to fancy bars etc and yeah maybe you can reach your 5k a month...

People have no clue / are not willing to experience adjustment for 3 weeks... But easily possible to live here for budgets mentioned above...