Hey Gavan, Better is come to NJP by train then book a cab to Gangtok. There are many local tourism offices at Mall road , Gangtok. You can book there and they will also arrange your permits. Rough itinerary : Day1 - Reach NJP and go to Gangtok Day2 - Local sight seeing of Gangtok Day3- Nathula Pass and Baba Barbhajan Mandir Day4&5&6 : North Sikkim tour Then you can go to South Sikkim, Darjeeling, Meghalaya and Tawang ( For Meghalaya and Tawang, you have to come Guwahati from NJP). Happy travelling!!!!