Gangtok was the part of our plan to visit the north east along with other cities.We went their by a sedan car which could be easily booked in daarjeeling.
Gangtok city is more like a continuous one buliding township along the hills curves.It was well equiped with lastest facilities and food joints like dominos and malls.So you wouldnt worry their about your buying needs.
Advice- keep an umbrella in hand during your walks in city as it rains their almost everyday wothout a warning.We were casual and didnt take them.Got wet from top to bottom!
The whole focus of your plans of visiting various places should be nature.You wouldnt enjoy the temples as much as you would the botanical gardens and roaming in the lap of nature.Avoid going to amusement parks and other adventure sports their if you have planned a joint trip of many cities altogether.Focus on enjoying and rejuvenating in nature.