Depends on the locations where you will be. To be more specific: it depends on what city/province you will stay in. Each regions has its own must-see spots, as well as lesser-known exotic areas. If you have the time, try venturing out a bit. Since most of the famous and beautiful spots are being heavily commercialized, it would be good if you can keep to the fringe areas of those spots and you’ll likely discover nice places with hardly anyone around. And do so during week days instead of the weekends. Off the top of my head in no particular order, in South VN: Nha Trang beaches with Yen island (swift nests), Hoi An, Mui Ne sand dunes, Tay Ninh, Ca Mau swamp land, Vinh Long, Pleiku, Hue, Quang Tri. I’d definitely skip Cu Chi.
I don’t know in what professional capacity you’re going there, but I don’t think you’ll be able to discern the tension between the two regions. As for the relationship between VN and China, officially I would use “polite” to “cordial” to describe it, but unofficially it can be said to be ranging between ambivalence to disdain.
I think you’ll have no problem asking questions about diabetes since it is recognized as a natural illness by the majority of Vietnamese, but with HIV it’s a difference matter. As with any secretive society, HIV is considered a social disease with shameful associations. When asking questions about HIV, keep them in general sense, avoid the specifics (“Do you know anyone who has HIV?” type of questions) and when in doubt stick to double meaning, indirect method of questioning that open to comparison. This applies to both formal and informal situations. Also keep in mind that the level of knowledge of HIV is quite low in the populace over there.
Unless being offered such foods, you can just skip those places that only serve those dishes. If you’re offered such dishes in an informal setting, just be honest and tell them your conditions and decline. If you want to be smooth, say that you often have those dishes in the US so you’d wish to sample other foods instead. (That always get me off the hook). But in formal settings, you’re stuck.
As for software, I like mViet since it covers all other typing methods of other software such as VNI, VPS and it uses Unicode fonts (which come with Windows 2000 and above) and so you don’t have to download specialized fonts. You can get it here. You must have software in order to type in Vietnamese.