Are the Vietnamese friendly?
Well, I'm Korean and I have absolutely no problems with Viets. I think that they are friendly and nice. I do have a Viet friend and she's pretty awesome.
There are several ways one of which is "Chào thân ái". This literally means "Warm greetings" but I believe it serves well as the Vietnamese equivalent of "Best wishes". Please also note that this phrase sounds quite friendly and so is widely used in a range of formality, sometimes in official letter. Source: I am a Vietnamese.
Sino-Vietnamese vocabulary is a part of the Vietnamese language. So, yes. Vietnamese know a lot of 'Sino-Vietnamese' as 50-60% of Vietnamese consists of words of Chinese origin or Sino-Vietnamese. For example, the word 'at' is Tai in Vietnamese (from 在 'Zai' in Chinese), to come in Vietnamese is 'Lai' (same as in Chinese 来 'Lai'), country is Quoc in Vietnamese (from 國 Gwok in Cantonese), and the list could co on for hundreds and thousands…