Seeking advice on Sikkim/Darjeeling/Assam/Orissa

I'm planning my 5th trip to India for this December. I have a month and will spend the last 2 weeks in parts of Tamil Nadu (from Chennai down to Thanjuvar area). My question is about the first 2 weeks, which I want to spend in areas new to me. My idea is to fly to Bagdorga and explore Darjeeling and vicinity. Then fly to Guwahati and explore areas along the Brahamaputra River Valley area, especially temples and other attractions from Guwahati to Tezpur (not further east then that). Then fly to Bhubaneswar (Orissa) and there seems to be a fairly manageable triangle area (including Puri) to be explored there before flying out to Tamil Nadu. There seem to be surprisingly easy plane connections available between the 3 areas (and also to Chennai), saving time.

Is this too much for 2 weeks? If so, which would you exclude? (I'm thinking Assam/Guwahati, but that's where the weather is really perfect, escaping Michigan winter but not too hot.) I know Darjeeling will be cold, but it seems to be bright and sunny that time of year and could even get lucky and be around 60 (F.) but average high in December is 47.

I'm mostly focusing on culture and just light hiking (due to a leg injury). Any and all suggestions appreciated, both about the reasonableness of my plan and any highlights I might not be thinking of (and perhaps not in the guide books).

I think that the three areas you want to visit in the North make it a very hectic trip.
Better is to select just two of them.

We like to travel in a slow tempo and enjoyed our fortnight in the Guwahati - Jorhat - Tezpur area.
Details you find in he March part of the 2010 journal in my signature,

I agree with vonkla that it is a trifle hectic. You could do a quick tour of North Bengal and Sikkim instead.

Or just concentrate on the Orissa part, with Puri, Konark, Bhubaneshwar, and add on Koraput in the hinterland.

Or, stick to Assam (Guwahati etc) and add on Meghalaya.