I can't speak to MS, but I do have atherosclerosis/peripheral vascular disease so can address your question about circulation issues.
About three years ago my vascular surgeon was absolutely delighted to hear that I had stopped smoking and switched to vaping. You always hear that nicotine is a vasoconstictor, but that is only a short term and temporary effect, and is not the cause of the circulatory health problems associated with smoking. The main culprit in smoking's deleterious effect on circulation and diseases like atherosclerosis (and this is according to the doctor himself) is the carbon monoxide!
Besides speaking to my doctors about this issue, I have also seen very reassuring discussions of nicotine and its cardiovascular impacts in published scientific materials - mainly research into smokeless tobacco products like snus, and also research into the use of FDA approved NRT products. The bottom line is that nicotine, when delivered without the smoke (and of course without the carbon monoxide), does not present cardiovascular concerns. Here are some quotes and references for you:
Specifically regarding smokeless tobacco products:
"In 2003, Asplund completed a comprehensive review of the cardiovascular effects of ST use [102]. He concluded that, in distinct contrast to smokers, ST users do not exhibit any significant differences from nonusers of tobacco with regard to the following measures of cardiovascular health: heart rate, blood pressure, cardiac output and maximal working capacity, levels of hemoglobin and hematocrit, leukocytes, antioxidant vitamins, fibrinogen, components of the fibrinolytic system, C-reactive protein and thromboxane A2 production.
In addition, ST users did not show important smoking-associated vascular changes, including increased thickness of blood vessels and atherosclerotic plaque development. In summary, most of the medical and epidemiologic evidence documents that ST users do not have elevated risks for cardiovascular diseases."
http://www.casaa.org/files/THR.pdf
Regarding nicotine as delivered in NRT products:
"Smokers smoke because they are addicted to nicotine in cigarettes," said Dr. Daines. "But it is the smoke, not the nicotine, which causes a long list of diseases, including lung cancer, heart disease, stroke and emphysema."
"Nicotine is the addictive ingredient in cigarettes that keeps smokers hooked, but it's not the ingredient that harms smokers' health," emphasized Ursula Bauer, Ph.D., M.P.H, director of the state's Tobacco Control Program. "With safe nicotine products, smokers can give up the smoke without giving up the nicotine."
"As smokers become more familiar using other nicotine products, like patches, gum and lozenges, they will find themselves less interested in smoking cigarettes. Over time, more smokers will quit. Right now, the FDA is standing in the way of smokers' easy access to safe nicotine products," said Jonathan Foulds, Ph.D., Associate Professor and Director of the Tobacco Dependence Program and the University of Medicine and Dentistry of New Jersey.
"Many smokers are confused about the safety of nicotine patches, gum and lozenges, mistakenly believing that nicotine causes cancer or that patches are more likely than cigarettes to cause a heart attack. By educating consumers and making these products more widely available, smokers will begin to see them as real alternatives to cigarettes and a product they can use to quit smoking altogether,"said Gary Giovino, Ph.D., Professor of Health Behavior and the University at Buffalo.
Health Commissioner Petitions FDA to Make Over-the-Counter Nicotine Therapies as Easy to Buy as Cigarettes
More generally:
If people have difficulty overcoming both nicotine dependence and long-term habit change, then surely the solution is to help them avoid most of the health risks with only a minimal alteration in their nicotine-seeking habits. This implies a nicotine replacement device which looks like a cigarette and delivers cigarette-like boli of nicotine,
but does not deliver the tar and carbon monoxide which cause the vast majority of smoking-related disease . . . the development and promotion of such a product (and its eventual replacement of tobacco) could have massive beneficial public health implications lasting into the 21st century".
Commentary on Etter & Bullen (2011): Could E-cigs become the ultimate nicotine maintenance device? - FOULDS - 2011 - Addiction - Wiley Online Library