Thanks very much for your super-quick response Arico!
I think I should clarify that the plan is for the tomatoes grow directly horizontally out of the box that contains the soil, rather than growing upward then bending to the side. I've never seen examples of this, but I know tomatoes can be grown upside down, and of course rightside up, so I figure horizontal should be possible too. Perhaps this will address your concerns of both the stalks snapping, and the leaves growing above the windblock. Even so, you might be correct that they're too close to the top of the windblock.
Regarding evaporation from the planting medium, maybe it's not clear from the diagram but I plan to put a lid on the soil box, so the only significant route of evaporation would be through the slots that the stakes stick out of.
