There are no major side effects known to be caused directly from vaping, except that a very small fraction of customers may be allergic or sensitive to propylene glycol (PG), which simply creates some irritation in the throat. All known side effects are typically associated with cigarette withdrawal and the body's transition, and are not due to vaping itself.
No, nicotine does not and has never caused cancer. Nicotine used in vape juice, e-cigarettes and other vapes is the same grade as typically found in NRT patches, gums, and sprays. It has never found to be carcinogenic. Nicotine via traditional cigarettes are highly carcinogenic due to combustion. Vaping avoids all combustion.
The type of device and how you care for it are major factors in how long your e-cigarette will last.
Preferably, you should use no nicotine. However, if you cannot do without nicotine, it is recommended to start off with enough nicotine to satisfy your craving and then wean yourself down and, ultimately, off. This is not medical advice and simply opinion based on anecdotal information from customers and users.
Nicotine strength varies from person to person based on their individual smoking habit (type of cigarettes, length of puff, time smoke is kept inside lungs, etc.). It also varies based on device (how much vapour is produced will change how much nicotine gets delivered). However, we have some guidelines for consideration based on anecdotal data. It is important to select the correct nicotine strength that works for you. Each flavour comes in a variety of strengths.