It will be available that way, not sure if there's an extra charge for it. I seem to remember with GC1, there was a small one just to cover S&H.
I'm not sure. Not like there's anything important or even interesting in the box. Most games now adays, you get a keyboard shortcut foldout, a "quick install" guide, and everything else is on the CD. Sometimes you don't even get jewelcases.
Size of the beta? Size in what respect? amount you need to download? I don't think that the current Beta will be a good indication of the final size of the retail version of GC2, as a lot of the movies and such aren't in GC2 yet. Number of people? Probably a not-insignificant portion of the people that will be playing GC2 on or near the release date. Unlike many betas, users in stardock betas have a very good chance of getting their feedback listened to, or even their suggestions implemented, which increases the number of people that want to be in the beta. Also, the fact that anyone that had total gaming when total gaming switched over to tokens will be able to join the beta means that the entry barrier to the beta is quite low.