Hi Anshuk, Gangtok is a nice choice for your first solo trip. The views are obviously scenic, Sikkim is a very safe location with an extremely low crime rate, so do not worry about your safety, having said do not take things (and nature) for granted. Most of our safety is in our hands, so keep a check on your bus/train timings and travel responsibly. I have attached a couple of articles for a better insight of Gangtok and solo travel.