I am sure you have already heard of so many places in east Sikkim and must be wondering how many number of days are actually needed to cover the entire Silk Route in Sikkim. I had the same question when I first went to the region in Sikkim. I had the same doubts and the same queries which you have now on Silk Route.
On my first visit I just took 3 days to cover the entire Silk Route. Yes, it can be covered in 3 days only if you have less time in hand. There is no need to stay at all places rather you can stay at 2 places between NJP/Siliguri and Gangtok. But then after with each trip I started adding up places on my list and the number of places has been increasing till date with all my east Sikkim trips. Last 3 times in Sikkim I spent visited east Sikkim exclusively. The trips were focused on east Sikkim only covering the Silk Route. So it is totally up to you how many days you would need to cover Silk Route. At least 2 nights are required to explore Silk Route in east Sikkim.
NJP/Siliguri/Bagdogra to Gangtok via Silk Route
There are actually 2 routes to visit east Sikkim from this side. If I join all places of interest in an order which have accommodation facility, I can draw the below 2 paths:
Route 1: NJP/Bagdogra/Siliguri >> Rongpo >> Rongli Bzar >> Lingtam >> Padamchen >> Zuluk >> Lungthung >> Gnathang Valley >> Gangtok
Route 2: NJP/Bagdogra/Siliguri >> Kalimpong >> Ramdura >> Ichegaon >> Sillery Gaon >> Pedong >> Rishikhola >> Aritar >> Rongli Bazar >> Lingtam >> Padamchen >> Zuluk >> Lungthung >> Gnathang Valley >> Gangtok
Gangtok to NJP/Bagdogra/Siliguri via Silk Route
You get the same path until Rongli Bazar – the border between West Bengal and Sikkim. You can proceed to NJP/Bagdogra directly from Lingtam via Rongli and Rongpo else you can take the diversion via Aritar, Rishikhola, Sillery Gaon, etc. and spent more nights there.
People who have already visited Gangtok and want to visit Silk Route exclusively, it is quite easy to skip Gangtok and frame a travel plan. I would suggest you to visit east Sikkim directly from NJP/Bagdogra. If you visit from this way Gnathang Valley will be the last point to spend night. From Gnathang you can explore all sightseeing along Silk Route and return to Gnathnag for night stay and then proceed back towards NJP/Bagdogra exploring other interesting places as you select from the list given above.
You can just drop a comment in the comment box below or mail me at firstname.lastname@example.org for any information you want on Silk Route travel plan. I will surely revert back. I would be more than happy to see your feedback on my Facebook page (review section). Stay tuned for more details on Sikkim.