I think you're underestimating it.
Look at Wii Sports Resort's start in comparison to Mario Kart Wii; it's nearly selling as much as Mario Kart Wii did. And that's in a time of lower Wii sales.
I would say it has a chance of selling close to Mario Kart Wii levels, and MKWii should end in the 30-40 million range.
As for WSR's sales by march:
It's selling ~ 200K pr week now. That's what MKWii entered with last year, and it sold 4.8 million from here on and in last year. Wii Sports Resort should be at ~ 9.5 million by the end of the year. Then 2 million for the first quarter sounds correct (150K/week).
11-12 million seems fair.