It's a fusion reactor, so how do you get the water into the part with the hot stuff? That's all inside a magnetic field, I think. Also, you have to consider the neutron radiation's effect on the pipes that carry the water into the core, it's going to activate several metals in there, and cause weakening of the pipe wall, which will necessitate inspections and replacements.
It's a way harder engineering problem than you're letting on. Your comment is like a software user saying "How hard could it be just to add feature X?".
The heat transfer is not (will not be) directly from the plasma to the water. The fusion neutrons will impact a "blanket", which is water-cooled, and kept at a temperature of around 600-800 C. Weakening of the pipes and all other structural components will primarily be from neutron irradiation. Not to say that any of it's easy, just not for the reasons you suppose. :)
Exactly! Unlike in a fission reactor, where you can flow the coolant through the core, in a fusion reactor the energy has to be radiated through the surface of the reactor. The square/cube law comes into play: the surface area you can radiate through goes as r^2, while volume (and cost) of the reactor goes as r^3.
It's a way harder engineering problem than you're letting on. Your comment is like a software user saying "How hard could it be just to add feature X?".