The previously discussed round loop through Sikkim covering Zuluk and Nathula Pass has to be revised as Foreign citizens are not granted permission to visit either of the 2 towns.
The Furthest one can travel is Tsomgo Lake passed Gangtok, which requires a day pass.
The route might have to be completely scraped and a much cleaner pass through Darjeeeling and opting to go to Paro in Bhutan would seem to be a less stressful journey.
Bhutan shares a similar terrain to Sikkim and with not much of restrictions for Foreign citizens it seems to be the best approach except for border crossing .