>The only issue I have is gravity. I dunno how much trust I would
>place in artificial gravity generators, and without knowing a bit more
>about the material used to construct the shell (and presumably, the
>'bedrock' of the continent), I can't do the math to figure out how
>much of that is needed to produce a Earth-like gravitational field.

If it's on the inside of the sphere? An infinite amount. Mass _above_ you on a sphere doesn't contribute either way to the gravitational pull -- only mass below you does.