There are many 'ex-pat' schools in both Ha Noi and HCMC and there are equally as many quality standards, too.
I suggest that you would be best served by checking out the schools after you arrive. Your embassy - easily spotted by the two large dumpsters filled with concrete blocks outside - can possibly offer guidance.
My daughter goes to a Vietnamese school and the education in it is good and she now communicates in Vietnamese fluently and has many local and ex-pat friends.
Ha Noi weather is temperate and its winters can be cool - just above 0C - so make sure you bring both warm clothing AND rain clothing - including PANTS which are needed when you ride motorcycles in wet weather - and don't forget get an International Driving Licence before you leave the States.
Voltage is 220VAC and you can buy 110/220/110 transformers in the markets.