Visas: This is the difficult part. If you're from the US or South Korea you can pretty much forget about it. Mt Kumgang however is the one exception with visa free exemptions for most nationalities. Other nationals may have some luck approaching the tourism office in the North Korean Embassy in Beijing; your chances of being granted a visa are far lower at other embassies. A visa, if it is going to be granted, can normally be granted quickly.
Health risks: No particular risks, although there is a shortage of western medicines so it's not a great place to get sick. However traditional Korean medicine is available.