I don't think it will be over 500k, it would be if they had produced more.
When does it get released?

I'll go with about 650,000

200k in the 1st week

based on the way hardcore wii games sell in japan these days.

^hahahaha...ohh wait your not kidding b/c it could happen

 21th of Januray in Japan.

And I think 350k first week in Japan. But that's just because home consoles and games aren't selling very well in Japan, atleast not at this time. 

its delayed (10 days wasn't it) so then it would come out the 31th of January

 ontopic: I think it will sell about 650.000 firstweek becouse we already know the first shipment is smaller than galaxy (well actually now I think about it, they can refill them trough to whole week afcours, so it might be more).

In the us I think it might even sell over 2 million first week and in Europe over 1 million. 

According to some infos from intra-distribution, First Shipments will be about 500k.

(Of cource, the range of number varies from infos, probably it won't be more than 600k)

 I don't think 2 million in NA or 1 Mil in the EU is accurate , Half that estimate and I might agree with you.

Will there be restocking, throughout the remaining 3 days, if SSBB would sell out?

 Well maybe not, but I know a lot of people who played melee will be bying it the minute it releases, there is no way these people wouldn't know it comes out in march. I think they all are pretty hardcore (there will be lot of ads too).