
There is, indeed, a cafe. I checked out the place today. Incidentally, I wasn't expecting much as far as the art was concerned and was pleasantly surprised--it's really quite an interesting installation. And the building is much larger and nicer inside than I had expected. All in all a really worthy addition to the SF museum scene. And there is a second floor window that looks directly down on the food prep area of the cafe--I watched some guy making a Caesar Salad. I'm not sure if that's Libeskind's idea of living art or just an interesting design quirk, but it's fun to watch.
As for the plaza, a lot of it is taken up by a water feature (infinity pool, low waterfalls etc). But there are nice benches and some outdoor tables directly in front of the cafe area.