I'm a British birder living in India, and did a 3-week NE India trip last year. A little bit later than you at end of March/April, but visiting the main areas (west to east) in Assam and Arunachal Pradesh of Eaglenest Wildlife Sanctuary, Nameri National Park, Kaziranga National Park and Mishmi Hills. These are the most obvious sites to do, along with Manas or Namdapha National Parks. All have fantastic birding.
Most birders tend to visit between late March and May which gets most of the summer migrants and is easier for several of the specialities as birds are singing and more obvious generally with breeding activity underway. You would have all winter migrants (Black-necked Crane being a notable one that leaves in mid February) and still find many of the specialities (e.g. Beautiful Nuthatch, Blackish-breasted Babbler (Sikkim Wedge-billed), Fire-tailed Myzornis, Ward’s Trogon, Bugun Liocichla), but miss the summer migrants, and might find some of the other species, such as wren-babblers, extra skulking when they aren't singing!
It would also be cold, and some of the higher areas (such as Sela Pass, above Eaglenest) might be inaccessible.
I'd suggest you do some research on these key sites - if you have just two weeks it's not possible to include both Eaglenest and Mishmi Hills - and work out any preferences. Feel free to send me a message, or email
[email protected], if you want to discuss further.